67
Pain, 50 (1992) 67-73 0 1992 Elsevier Science Publishers B.V. All rights reserved 0304-3959/92/$05.00
PAIN 02068
The Pain Anxiety Symptoms Scale: development and validation of a scale to measure fear of pain Lance M. McCracken ‘qb,Claudia Zayfert a and Richard T. Gross b*c a De~art#lent
of Psychofogy, West Virginia U~~l~ersi~, ~o~a~town, and c Department
ofAnesthesiology,
WV 265~6-#4U
IUSAI,
’ De~~t~ent
of BehaL,j~raf ~edicjne
West Virginia Unioersity Health Sciences Center, Margantown,
WV26506
and ~~chjat~,
(USA)
(Received 29 July 1991, revision received 30 December 1991, accepted 9 January 1992)
Fear of pain has been implicated in the development and maintenance of chronic pain behavior. Summary Consistent with conceptualizations of anxiety as occurring within three response modes, this paper introduces an instrument to measure fear of pain across cognitive, overt behavioral, and physiological domains. The Pain Anxiety Symptoms Scale (PASS) was administered to 104 consecutive referrals to a multidisciplinary pain clinic. The alpha coefficients were 0.94 for the total scale and ranged from 0.81 to 0.89 for the subscales. Validity was supported by significant correlations with measures of anxiety and disability. Regression analyses controlling for measures of emotional distress and pain showed that the PASS made a significant and unique contribution to the prediction of disability and interference due to pain. Evidence presented here supports the potential utility of the PASS in the continued study of fear of pain and its contribution to the development and maintenance of pain behaviors. Factor analysis and behavioral validation studies are in progress. Key words: Chronic pain; Pain behavior; Fear of pain; Anxiety; Disability; Pain assessment
introduction
Medical professionals are often frustrated by the intractable nature of chronic pain. This frustration results from the frequent failure of medical treatment and the persistence of pain, suffering, and disability in the absence of organic pathology (Wall 1979). Recently, Lethem et al. (1983) proposed an explanation of exaggerated or persistent pain behavior based on fear of pain. They pointed out that behaviora indicators of pain can become desynchronous with the organic/ sensory component of pain. In other words, verbal complaints of pain, reduced activity, and other observable expressions of pain can increase, decrease, or remain stable independent of changes in tissue damage. Specifically, Lethem et al. (1983) addressed the problem of behavioral indicators of pain that persist as
Correspondence to: Richard T. Gross, Ph.D., Department of Behavioral Medicine and Psychiatry, West Virginia University Health Sciences Center, Morgantown, WV 26506 (USA)
tissue damage decreases or remits. They attribute this persistence of pain indicators to the emotional response to pain. According to their model, as with other fears, avoidance associated with fear of pain leads to greater fear and to increasingly limited activity. As tissue injury remits and fear remains, pain behaviors are no longer elicited by an internal sensory stimulus but rather become largely avoidance responses maintained by subsequent reduction of emotionai distress. Recent data support the analogy between pain behaviors and fear behaviors. For example, Phillips and Jahanshahi (1985) demonstrated that when chronic pain patients were exposed to an aversive stimulus, avoidance led to increased sensitivity to the pain stimulus and increased avoidance on subsequent trials. Phillips (1987) suggested that avoidance in chronic pain sufferers may be related to beliefs and memories of the sufferer which lead to expectations that pain wiI1 increase following exposure to .pain-related stimuli. If this model is correct, processes which explain the modification of fear and anxiety, such as habituation, sensitization, and disconfirmation may also be applicable to
68
understanding changes in pain behavior as well (Phillips 1987). In a related area, several researchers have chosen to examine the relationship between anxiety and pain. Studies of the effects of induced anxiety on responses to acute laboratory pain stimuli suggest that anxiety related to pain increases ratings of perceived pain intensity (Weisenberg et al. 1984; Cornwall and Donderi 1988; Al Absi and Rokke 19911 while anxiety unrelated to pain increases pain tolerance (Bobey and Davidson 19’70) and decreases galvanic skin responses to pain (Weisenberg et al. 1984). Results of Arntz et al. (19911 suggest that attention to pain increases the impact of pain and that anxiety about pain directs attention to pain. Researchers have afso suggested that pain-related anxiety may influence the emotional response to pain (Cornwall and Donderi 1988) and thus may increase what Fordyce (1976) refers to as the suffering component of the pain experience. Recognizing the importance of emotional and cognitive responses to pain in determining the extent of suffering experienced by pain patients, researchers have developed a variety of measures to assess these responses indirectly. Thus, self-report measures of patient behavior in response to pain evaluate subjective aspects of the pain experience such as negative cognitions (Cognitive Error Questionnaire, Lefebvre 1981; Inventory of Negative Thoughts in Response to Pain, Gil et al. 19901, adaptive and maladaptive thoughts (Pain Cognitions Questionnaire, Boston et al 19901 positive and negative cognitive and overt behavioral pain coping strategies (Coping Strategies Questionnaire (CSQ), Rosenstiel and Keefe 19831, and beliefs and attitudes associated with functional impairment (Pain and Impairment Relationship Scale, Riley et al. 1988; Slater et al. 1991). While these are clearly important dimensions to assess, they do not yield information which directly pertains to pain-related anxiety and which would further our understanding of its role in the chronic pain experience. There has been one attempt to assess fear responses to pain in chronic pain patients. This was a 6-item Fear Self-Statements subscale included in an expanded version of the CSQ (Gil et al. 19891. In their study of patients with pain from sickle cell disease, Gil et al. (1989) found that high scores on a negative thinking and passive adherence coping factor (which included the Fear Self-Statements subscale) predicted greater severity of painful episodes, lower Ievels of activity, more psychological distress, and more frequent health care utiiization. The numerous self-report measures discussed above. including the CSQ Fear Self-Statements subscale of Gil et al. (19891, focus on ~ognitions only. With the exception of the CSQ, which includes behavioral pain coping responses, these commonly used measures de-
vote little or no attention to overt behavioral and physiological responses to pain which are of particular interest in the study of anxiety states. This paper describes the development of a self-report instrument, the Pain Anxiety Symptoms Scale (PASS), to measure fear of pain. This measure is intended to provide a means of evaluating the importance of fear of pain in exaggerated or persistent pain behaviors. As a research tool, it may prove useful for classifying pain patients with respect to their level of pain-related anxiety. This information will, in turn, allow examination of how anxiety responses interact with other factors to enhance the experience of pain. Furthermore, it may facilitate development of individuahzed treatment inte~entions based on the degree to which fear is a component in an individual’s pain experience. Thus, as we gain a better understanding of the role of anxiety in clinical pain, this instrument may have important clinical utility as well. This instrument may also contribute to available measures of pain behavior by broadening the scope of assessment to include physiological and motoric response domains. Consistent with the Three-Systems Model of fear (Lang 1968; Hugdahl 19811, this instrument assesses fear of pain behaviors in 3 response modalities: cognitive, physiologic and motoric. Thus, patients are asked to respond to items which describe (a> fearful thoughts and ruminations about the consequences of their pain, (b) physiological symptoms of fear associated with the experience of pain, and (c> avoidance and escape of activities which they believe may increase pain. Such a tri-modal assessment of fear of pain will facilitate its study within the current framework employed in the study of anxiety disorders. For exampie. it has been shown that individuals who report specific fears (i.e., phobias) often show discordance or desynchrony of response modalities in the expression of their fears (Hodgson and Rachman 1974; Rachman and Hodgson 1974). Similarly, fear of pain may be expressed disproportionately among the 3 response channels, and behaviors of these separate channels may respond differently to inte~entions. If, like other phobias, fear of pain exhibits individual differences in the dominant response channel, the information gleaned from a multimodal assessment may have important implications for treatment of chronic pain problems.
Method Subjects The subjects were 104 outpatients (48 males, 56 females) evaiuated consecutively at a multidiscipljna~ pain management center. Mean age of the sample was 45.0 years (SD. = 13.4). Seventy-five percent of the patients were married, 12% single, 9% divorced. and
69 4% widowed. Mean years of education was 12.0 (SD. = 2.3). The majority of patients presented with back pain (69%), but the sample also included patients with extremity, facial/head, and torso pain complaints. Pain complaints were chronic in nature. All patients reported pain that persisted despite multiple medical interventions. The mean duration of pain was 63.1 months (SD. = 105.8). Forty percent of patients had undergone at least 1 pain-related surgery, and 52% were taking narcotic analgesics on a regular basis. The PASS was administered as part of a comprehensive pain assessment procedure. Patients completed the PASS and other standardized inventories at home several weeks prior to their scheduled appointment in the pain management center. The standardized inventories included commonly employed measures of depression, anxiety, pain, and disability and are described below.
Measures PASS. The initial scale consisted of 62 rationally derived items generated to assess fear of pain in each of the 3 response modes. Items were modeled after items of commonly used anxiety measures and the criterion for item inclusion was a logical rather than empirical relationship with the fear of pain construct. Item content represented anxiety symptoms frequently described in the anxiety disorders literature and patients’ descriptions of their fears related to pain. Items were developed for inclusion in 4 subscales. The 1st subscale, Fear of Pain (19 items), was intended to measure fearful thoughts related to the experience of pain or anticipated negative consequences of pain. The 2nd subscale, Cognitive Anxiety (10 items), was designed to assess cognitive symptoms related to the experience of pain, such as racing thoughts or impaired concentration. The 3rd subscale, Somatic Anxiety (16 items), assessed symptoms reflecting physiological arousal related to the experience of pain. The 4th subscale, Escape and Avoidance (17 items), assessed overt behavioral responses to pain. Table I shows sample items for each of these subscales.
Patients were instructed to rate the frequency of occurrence of each of the 62 behaviors on a 6-point scale from 0 ‘never’ to 5 ‘always’. The total score was computed by reversing 11 negatively keyed items and summing the ratings across the entire measure. Subscale scores were computed by totaling responses to items designated for each subscale. Beck Depression Incwntory (BDI). The BDI (Beck et al. 1961) is a 21-item, self-report measure of depression. It assesses common cognitive and vegetative symptoms of depression. More than 25 years of research evaluating the psychometric properties of the BDI has indicated that it has excellent reliability and validity (Beck et al. 1988). Cognirive Somatic Anxiety Questionnaire (C&IQ). Symptoms of anxiety were assessed with the CSAQ (Schwartz et al. 1978). The CSAQ consists of a list of 14 symptoms of anxiety, including both cognitive and somatic aspects. Respondents are asked to rate the degree to which they experience each of these symptoms when they are anxious. Factor analyses of the CSAQ have identified distinct somatic and cognitive factors (Steptoe and Kearsley 1990). The scale yields separate scores for each of these aspects. Coping Strategies Questionnaire (CSQ). The CSQ (Rosenstiel and Keefe 1983) is a 42-item questionnaire which assesses self-reported use of 7 different cognitive and behavioral pain coping strategies. Only the Catastrophizing subscale was calculated for this study. This ‘6-item scale assesses negative thinking in response to pain. McCiN Pain Questionnaire (MPQ). The MPQ (Melzack 1975) consists of 20 subclasses of 78 adjectives divided among 4 dimensions: sensory, affective, evaluative, and miscellaneous. The purpose of the MPQ is to provide quantitative indices of the subjective pain experience. It has become the most widely used measure of pain and has demonstrated acceptable reliability and face, construct, discriminant, and concurrent validity (Reading 1983). The MPQ yields several variables including scores for each of the separate dimensions and a total score. Mu~tidimensionnl Pain Inventory (MPI). The MPI (formerly the WHYMPI, Kerns et al. 1985) is a brief, comprehensive measure of important aspects of the subjective experience of chronic pain based
TABLE I SAMPLE ITEMS FROM THE PAIN ANXIETY SYMPTOMS SCALE (PASS) Subscale
Item content
Somatic anxiety
I become sweaty when in pain. Pain seems to cause my heart to pound or race. When I sense pain, I feel dizzy or faint. I have pressure or tightness in my chest when in pain. I can stay relaxed when I hurt.
Cognitive Anxiety
I feel disoriented and confused when I hurt. When I hurt, I think about the pain constantly. I am bothered by unwanted thoughts when I’m in pain. My thoughts are agitated and keyed up as pain approaches. During painful episodes it is difficult for me to think of anything besides the pain. I worry when I am in pain.
Fear
I think that pain is a signal that means I am damaging myself. I dread feeling pain. When pain comes on strong, I think that I might become paralyzed or totally disabled. I am afraid that I will have more pain if I am not careful. I think that if my pain gets too severe, it will never decrease.
Escape/Avoidance
When I feel pain I try to stay as still as possible. I try to avoid activities which cause pain. As soon as pain comes on I take medication to reduce it. I seek reassurance that I am OK during times of more severe pain. I go immediately to bed when I feel severe pain.
Note: subjects respond to each item by selecting a frequency rating from 0 ‘never’ to 5 ‘always’.
70 TABLE
II
SUMMARY
STATISTICS
FOR PASS SUBSCALES
AND TOTAL
SCALE
SCORES
Subscale
No. of items
Item means
S.D.
Alpha
I
2
3
Somatic Cognitive Fear Est./Avoid
14 10 14 15
1.73 2.56 2.21 2.54
1.12 1.10 1.04 0.92
0.89 0.87 0.85 0.8 I
0.68 0.64 0.48
0.70 0.5 I
0.45
Total
53
2.24
0.88
0.94
0.85
0.86
0.85
“ All correlations
significant
” 4
0.74
at P < 0.001. N = 104
on the cognitive-behavioral perspective of chronic pain. The 52 items of the MPI divide into 3 major parts, each containing several subscales. The inventory examines the impact of pain on the patient’s life, responses of significant others to the patient’s pain behaviors, and level of participation in typical daily activities. Research with the MPI suggests that it has achieved adequate reliability, validity, and clinical utility (Kerns et al. 1985). Pain Disability Index (PDI). The PDI (Pollard 19841 is a 7-item, self-report measure which assesses patients’ perceived level of disability in 7 life areas. The PDI yields a total score, as well as factor scores for pain-related disability in discretionary and obligatory activities. Recent research has supported the factor structure, validity, and retest reliability of the PDI (Tait et al. 19901 and its construct validity (Jerome and Gross 1991). Spielberger Truit Anxiety Scale (STAI-T). The STAI-T (Spielberger et al. 1970) is a 20-item inventory which assesses individuals’ predisposition to judge situations as dangerous or threatening and to respond with increased levels of state anxiety. The scale is widely used and has been found to have high internal consistency as well as high retest reliability and expected correlations with personality based measures of anxiety such as the Taylor Manifest Anxiety Scale.
TABLE
Intercorrelations
Results Scale development and psychometrics
Preliminary analyses included examination of frequency distributions for item responses and corrected item-scale correlations (correlations of items with their respective scale scores computed with the item omitted). Based on these analyses, 1 item was eliminated because of a highly skewed distribution and 7 items were eliminated because they correlated more highly with a subscale other than the one for which they were written. In these cases, examination of item content indicated that these items were not conceptually similar to the other subscales. A final item was eliminated from further analyses because it was not significantly correlated (at P < 0.05) with any of the PASS subscales. The final inventory submitted to further analyses consisted of 53 items, 14 assessing somatic anxiety,
III
CORRELATIONS
OF
PASS
SUBSCALES
AND
TOTAL
SCORES
WITH
MEASURES
OF
PAIN,
ANXIETY,
DEPRESSION
DISABILITY PASS scores Somatic
Cognitive
Fear
Est./Avoid
Total
CSAQ Cognitive Somatic
0.49 ** 0.74 **
0.61 ** 0.55 * *
0.53 ** 0.56 * *
0.25 0.17
0.54 ** 0.61 **
McGill Sensory Affective STAI-T
0.45 ** 0.51 ** 0.52 **
0.26 * 0.33 ** 0.67 **
0.20 0.36 ** 0.53 **
0. I6 0.31 ** 0.29 *
0.31 ** 0.44 ** 0.60 * *
MPI Pain severity Interference
0.35 ** 0.28 *
0.25 * 0.33 **
0.28 * 0.31 **
0.18 0.36 **
0.32 * * 0.39 **
0.67 0.51 0.39 0.25
0.67 0.67 0.39 0.27
0.66 * * 0.50 ** 0.40 ** 0.19
0.42 ** 0.30 ** 0.30 * * 0.16
0.73 0.57 0.45 0.29
CSQ Catastrophizing BDI PDI Tranquilizer/anxiolytic
use
** ** ** *
Note: * P < 0.01, * * P < 0.001. All probability
** ** ** *
values are l-tailed.
** ** ** *
AND
71
10 assessing cognitive anxiety, 14 assessing fear, and 15 assessing escape and avoidance responses. Table II includes summary statistics for the 4 subscales and the total scale score. Cronbach’s coefficient alpha was computed for each scale demonstrating adequate internal consistency (see Table II). Scale intercorrelations indicate that the subscales significantly intercorrelate. Squaring the interscale correlations reveals that overlapping variance ranges from 0.20 to 0.45, indicating that each scale provides unique information. Construct validity
Construct validity represents the extent to which a test is demonstrated to measure a theoretical construct or non-operationalized variable. One way to provide evidence for construct validity is to examine the correlations of a measure with theoretically related measures. To assess the construct validity of the PASS, the relationships between the various PASS scores and measures of anxiety, pain, and maladaptive coping responses to pain were assessed with Pearson product-moment correlations (see Table III). The validity of the somatic and cognitive anxiety scales of the PASS is supported by higher correlations between reTABLE
spective somatic and cognitive factors of the CSAQ. Significance tests for differences between correlated TS confirmed the statistical significance of these results in comparisons of the correlations of the PASS Cognitive Anxiety and Somatic Anxiety subscales with the CSAQ cognitive factor (t (101) = 1.92; P < 0.05) and the correlations of these PASS subscales with the CSAQ somatic factor (t (101) = 7.61; P < 0.001). All PASS variables demonstrated higher correlations with the affective dimension of the MPQ than with the sensory dimension. Finally, the trait form of the STAI, the pain severity scale of the MPI, and the catastrophizing scale of the CSQ showed consistent significant correlations with PASS subscales, demonstrating predictable overlap between these concepts and the behaviors assessed on the PASS (see Table III). Concurrent validity
While construct validity involves theoretical considerations, it also is important to demonstrate the practical or criterion-related validity of a measure. In the case of the PASS, criterion-related validity can be assessed by examining correlations of the PASS subscales with patient outcome variables that it should
IV
RESULTS OF HIERARCHICAL REGRESSION ANALYSES EMPLOYING DISTRESS IN ADDITION TO THE PASS TOTAL SCORE AS PREDICTORS ENCE DUE TO PAIN (MPI) Dependent Step Interference Equation
variable
R2
Beta
COMMON MEASURE OF PAIN AND PSYCHOLOGICAL OF SELF-RATED DISABILITY (PDI), AND INTERFER-
St.2
Fchange
Probability
1 0.23 0.24
0.38 0.17
0.096 0.019
27.43 2.36
0.0000 0.12
STAI-T PASS Equation 3
0.11 0.17
0.17 0.28
0.018 0.052
11.54 5.46
0.001 0.02
MPQ sensory PASS Equation 4
0.008 0.15
- 0.030 0.39
0.0008 0.14
0.82 15.39
0.37 0.0002
0.18 0.25
0.33 0.28
0.10 0.070
20.47 8.76
0.0000 0.004
0.18 0.24
0.23 0.32
0.035 0.068
19.32 8.41
0.0000 0.005
STAI-T PASS Equation 3
0.12 0.21
0.11 0.38
0.008 0.094
11.70 10.44
0.0009 0.002
MPQ sensory PASS Equation 4
0.03 0.20
0.04 0.44
0.0015 0.17
3.03 20.39
0.085 0.0000
0.25 0.34
0.40 0.32
0.14 0.095
31.51 13.60
0.0000 0.0004
BDI PASS Equation
2
Pain severity PASS Disability Equation BDI PASS Equation
1
2
Pain severity PASS
72
predict. When criterion-related validity is evaluated by correlating measures administered at one point in time, this type of validity is referred to as concurrent. Concurrent validity for the PASS was assessed by examining the relationships between the PASS scores and common measures of disability and depression. Correlational analyses indicated that PASS scores related significantly to scores from the interference scale of the MPI, scores from the BDI, and self-rated disability as measured by the PDI. In addition, point biserial correlations between PASS scores and a dichotomous variable representing use of tranquilizing or anxiolytic medications indicated that the Somatic and Cognitive Anxiety subscales as well as the total score were positively related to use of these medications (see Table III). Next, a series of hierarchical multiple regression analyses were performed. These assessed the significance of the unique increment in variance accounted for by the PASS in the prediction of disability after controlling for various measures of pain and psychological distress. Dependent variables were the PDI total score and the interference scale of the MPI. Independent variables entered into the equations before testing for the contribution of the PASS included the MPQ sensory score, the MPI pain severity scale score, the BDI score, and the STAI-T score. Results are included in Table IV. With one exception the PASS scores significantly contributed to the prediction of disability and interference due to pain after controling for variance related to the other predictors. The squared semi-partial correlation coefficients indicate that, in those equations in which the PASS contributed significantly, it accounted for a unique portion of variance which ranged from 5.2% to 17%. It consistently accounted for more unique outcome variance than the STAI or the sensory dimension of the MPQ.
Discussion
Preliminary analyses support the reliability and validity of the PASS as a measure of pain-related fear and anxiety. High alpha coefficients suggest that the PASS and its subscales demonstrate good internal consistency. Interscale correlations demonstrate that subscales are meaningfully related but also provide independent information about fear and anxiety responses. Construct validity of the PASS was supported by moderate correlations with other measures of anxiety. Moreover, although 4 of 5 variables from the PASS correlate with the CSAQ factors at a moderate to high moderate level, results support a differential relationship between the Cognitive and Somatic subscales of the PASS and the respective cognitive and somatic factors of the CSAQ. This finding supports the con-
struct validity of these PASS subscales. All subscales and the total PASS score showed higher correlations with the MPQ affective dimension than with the MPQ sensory dimension, indicating that fear related to pain is not simply a function of the sensory experience of pain. The results also confirm the concurrent validity of the PASS in relation to measures of disability, depression, and medication use, all pervasive consequences of chronic pain. Correlation analyses revealed that painrelated fear and anxiety, as measured by the PASS, are significant predictors of disability and interference with daily activities due to pain. Regression analyses controlling for measures of pain and psychological distress revealed that, with one exception, the PASS made a significant unique contribution to the prediction of disability. The PASS was a much better predictor of disability and interference than the Sensory subscale of the MPQ. The PASS also proved to be a better predictor of disability and interference than a measure of general anxiety (STAI-T). Relative to a measure of emotional distress, i.e., the BDI, the PASS made a greater contribution to the prediction of disability but added little to the prediction of interference. Overall, these results suggest that the PASS predicts important patient outcomes and provides information which is not currently available from other commonly used measures. The validity results discussed above include a large number of significance tests, implying a possibly unacceptable level of chance findings. Three points are relevant to understand better this limitation of the data. First, variables from the PASS demonstrate consistent patterns of relations with other variables, suggesting that chance does not play an important role in the results. For example, both the CSAQ and the STAI-T are measures of trait anxiety. Although item content of these measures is different, both measures demonstrated similar relations with the PASS increasing confidence in these findings. Likewise, similarities between the variables assessed by the MPI Interference subscale and the PDI, and by the MPI Pain Severity subscale and the MPQ sensory factor, tend to increase our confidence in the correlational results. Second, examination of the probability values associated with most of our results reveals the majority of the results attain low probability values. Third, to help reduce reliance on possibly spurious results, a more conservative significance criterion was chosen for Table III. Overall, the findings discussed above suggest that fear of pain can be conceptualized as a multidimensional response which may contribute significantly to the chronic pain experience. Further investigations of the psychometric properties of the PASS should seek to establish the temporal stability of the measure, as
73
well as the behavioral validity of the Somatic and Escape/Avoidance subscales. For example, it will be important to demonstrate that high scores on these subscales are highly correlated with the physiological measures of arousal in response to pain, with clinical observations, and spouse reports of escape and avoidance behaviors. This latter point is crucial since the validity data presented here only include intercorrelations of self-report instruments. Shared variance related to the method of data collection may contribute to these correlations. Finally, factor analyses should be conducted in order to establish the factor structure of the PASS and its concordance with the intended subscales. Creating subscales with greater discriminant validity also would be valuable. Scale overlap, particularly between the Fear and Cognitive Anxiety subscales, may be reduced by examining factor results and further examining item-scale correlations to eliminate items that reduce subscale independence. The purpose of this instrument is to facilitate the study of pain-related fear and anxiety in chronic pain populations with the goal of improving treatment outcome. The PASS may be particularly useful in this respect if it enables clinicians to identify empirical subtypes of pain patients who may respond differentially to treatment interventions. For example, it is conceivable that individuals whose fear of pain is manifested primarily in the physiological response system may be more responsive to relaxation training than to attempts at cognitive restructuring. In order to determine whether the PASS is useful in distinguishing subgroups of patients, cluster analyses of the PASS on a broader sample of chronic pain patients are currently being conducted. References Al Absi, M. and Rokke, P.D., Can anxiety help us tolerate pain?, Pain, 46 (1991) 43-51. Arntz, A., Dreessen, L. and Merckelbach, H., Attention, not anxiety, influences pain, Behav. Res. Ther., 29 (1991) 41-50. Beck, A.T., Steer, R.A. and Garbin, M.G., Psychometric properties of the Beck Depression Inventory: twenty-five years of evaluation, Clin. Psychol. Rev., 8 (1988) 77-100. Beck, A.T., Ward, C.H., Mendelson, M., Mock, J. and Erbaugh, J., An inventory for measuring depression, Arch. Gen. Psych., 4 (1961) 561-571. Bobey, M.J. and Davidson, P.O., Psychological factors affecting pain tolerance, J. Psychosom. Res., 14 (1970) 371-376. Boston, K., Pearce, S.A. and Richardson, P.H., The Pain Cognitions Questionnaire, J. Psychosom. Res., 34 (1990) 103-109. Cornwall, A. and Donderi, D.C., The effect of experimentally induced anxiety on the experience of pressure pain, Pain, 35 (1988) 105-113. Fordyce, W.E., Behavioral Methods in Chronic Pain and Illness, C.V. Mosby, St. Louis, MO, 1976, 236 pp.
Gil, K.M., Abrams, M.R., Phillips, G. and Keefe, F.J., Sickle cell disease pain: relation of coping strategies to adjustment, J. Consult. Clin. Psychol., 57 (1989) 725-731. Gil, K.M., Williams, D.A., Keefe, F.J. and Beckham, J.C., The relationship of negative thoughts to pain and psychological distress, Behav. Ther., 21 (1990) 349-362. Hodgson, R. and Rachman, S., Desynchrony in measures of fear, Behav. Res. Ther., 12 (1974) 319-326. Hugdahl, K., The three-system model of fear and emotion: a critical examination, Behav. Res. Ther., 19 (1981) 75-85. Jerome, A. and Gross, R.T., Pain Disability Index: construct and discriminant validity, Arch. Phys. Med. Rehab., 72 (1991) 920-922. Kerns, R.D., Turk, D.C. and Rudy, T.E., The West Haven-Yale Multidimensional Pain Inventory (WHYMPI), Pain, 23 (1985) 345-356. Lang, P.J., Fear reduction and fear behavior: problems in treating a construct. In: J.M. Shilen (Ed.), Research in Psychotherapy, Vol. 3, American Psychological Association, Washington, DC, 1968, pp. 90-103. Lefebvre, M.F., Cognitive distortion and cognitive errors in depressed psychiatric and low back pain patients, J. Consult. Clin. Psychol., 49 (1981) 517-525. Lethem, J., Slade, P.D., Troup, J.D.G. and Bentley, G., Outline of a fear-avoidance model of exaggerated pain perception-I, Behav. Res. Ther., 21 (1983) 401-408. Melzack, R., The McGill Pain Questionnaire: major properties and scoring methods, Pain, 1 (1975) 277-299. Phillips, H.C., Avoidance behavior and its role in sustaining chronic pain, Behav. Res. Ther., 25 (1987) 273-279. Phillips, H.C. and Jahanshahi, M., Chronic pain: an experimental analysis of the effects of exposure, Behav. Res. Ther., 23 (1985) 281-290. Pollard, C.A., Preliminary validity study Pain Disability Index, Percept. Motor Skills, 59 (1984) 974. Rachman, S. and Hodgson, R., Synchrony and desynchrony in fear and avoidance, Behav. Res. Ther., 12 (1974) 311-318. Reading, A.E., The McGill Pain Questionnaire: an appraisal. In: R. Melzack (Ed.), Pain Measurement and Assessment, Raven Press, New York, 1983, pp. 55-61. Riley, J.F., Ahern, D.K. and Follick, M.J., Chronic pain and functional impairment: assessing beliefs about their relationship, Arch. Phys. Med. Rehab., 69 (1988) 579-582. Rosenstiel, A.K. and Keefe, F.J., The use of coping strategies in low back pain patients: relationship to patient characteristics and current adjustment, Pain, 17 (1983) 33-40. Schwartz, G.E., Davidson, R.J. and Goleman, D.J., Patterning of cognitive and somatic processes in the self-regulation of anxiety: effects of meditation versus exercise, Psychosom. Med., 40 (1978) 321-328. Slater, M.A., Hall, H.F., Atkinson, H. and Garfin, S.R., Pain and impairment beliefs in chronic low back pain: validation of the Pain and Impairment Relationship Scale (PAIRS), Pain, 44 (1991) 51-56. Spielberger, C.D., Gorsuch, R.L. and Lushene, R.E., Manual for the State-Trait Anxiety Inventory, Consulting Psychologist Press, Palo Alto, CA, 1970. Steptoe, A. and Kearsley, N., Cognitive and somatic anxiety, Behav. Res. Ther., 28 (1990) 75-81. Tait, R.C., Chibnall, J.T. and Krause, S., The Pain Disability Index: psychometric properties, Pain, 40 (1990) 171-182. Wall, P.D., On the relation of injury to pain, Pain, 6 (1979) 253-264. Weisenberg, M., Aviram, O., Wolf, Y. and Raphaeli, N., Relevant and irrelevant anxiety in the reaction to pain, Pain, 20 (1984) 371-383.
Pain, 50 (1992) 67-73 0 1992 Elsevier Science Publishers B.V. All rights reserved 0304-3959/92/$05.00
PAIN 02068
The Pain Anxiety Symptoms Scale: development and validation of a scale to measure fear of pain Lance M. McCracken ‘qb,Claudia Zayfert a and Richard T. Gross b*c a De~art#lent
of Psychofogy, West Virginia U~~l~ersi~, ~o~a~town, and c Department
ofAnesthesiology,
WV 265~6-#4U
IUSAI,
’ De~~t~ent
of BehaL,j~raf ~edicjne
West Virginia Unioersity Health Sciences Center, Margantown,
WV26506
and ~~chjat~,
(USA)
(Received 29 July 1991, revision received 30 December 1991, accepted 9 January 1992)
Fear of pain has been implicated in the development and maintenance of chronic pain behavior. Summary Consistent with conceptualizations of anxiety as occurring within three response modes, this paper introduces an instrument to measure fear of pain across cognitive, overt behavioral, and physiological domains. The Pain Anxiety Symptoms Scale (PASS) was administered to 104 consecutive referrals to a multidisciplinary pain clinic. The alpha coefficients were 0.94 for the total scale and ranged from 0.81 to 0.89 for the subscales. Validity was supported by significant correlations with measures of anxiety and disability. Regression analyses controlling for measures of emotional distress and pain showed that the PASS made a significant and unique contribution to the prediction of disability and interference due to pain. Evidence presented here supports the potential utility of the PASS in the continued study of fear of pain and its contribution to the development and maintenance of pain behaviors. Factor analysis and behavioral validation studies are in progress. Key words: Chronic pain; Pain behavior; Fear of pain; Anxiety; Disability; Pain assessment
introduction
Medical professionals are often frustrated by the intractable nature of chronic pain. This frustration results from the frequent failure of medical treatment and the persistence of pain, suffering, and disability in the absence of organic pathology (Wall 1979). Recently, Lethem et al. (1983) proposed an explanation of exaggerated or persistent pain behavior based on fear of pain. They pointed out that behaviora indicators of pain can become desynchronous with the organic/ sensory component of pain. In other words, verbal complaints of pain, reduced activity, and other observable expressions of pain can increase, decrease, or remain stable independent of changes in tissue damage. Specifically, Lethem et al. (1983) addressed the problem of behavioral indicators of pain that persist as
Correspondence to: Richard T. Gross, Ph.D., Department of Behavioral Medicine and Psychiatry, West Virginia University Health Sciences Center, Morgantown, WV 26506 (USA)
tissue damage decreases or remits. They attribute this persistence of pain indicators to the emotional response to pain. According to their model, as with other fears, avoidance associated with fear of pain leads to greater fear and to increasingly limited activity. As tissue injury remits and fear remains, pain behaviors are no longer elicited by an internal sensory stimulus but rather become largely avoidance responses maintained by subsequent reduction of emotionai distress. Recent data support the analogy between pain behaviors and fear behaviors. For example, Phillips and Jahanshahi (1985) demonstrated that when chronic pain patients were exposed to an aversive stimulus, avoidance led to increased sensitivity to the pain stimulus and increased avoidance on subsequent trials. Phillips (1987) suggested that avoidance in chronic pain sufferers may be related to beliefs and memories of the sufferer which lead to expectations that pain wiI1 increase following exposure to .pain-related stimuli. If this model is correct, processes which explain the modification of fear and anxiety, such as habituation, sensitization, and disconfirmation may also be applicable to
68
understanding changes in pain behavior as well (Phillips 1987). In a related area, several researchers have chosen to examine the relationship between anxiety and pain. Studies of the effects of induced anxiety on responses to acute laboratory pain stimuli suggest that anxiety related to pain increases ratings of perceived pain intensity (Weisenberg et al. 1984; Cornwall and Donderi 1988; Al Absi and Rokke 19911 while anxiety unrelated to pain increases pain tolerance (Bobey and Davidson 19’70) and decreases galvanic skin responses to pain (Weisenberg et al. 1984). Results of Arntz et al. (19911 suggest that attention to pain increases the impact of pain and that anxiety about pain directs attention to pain. Researchers have afso suggested that pain-related anxiety may influence the emotional response to pain (Cornwall and Donderi 1988) and thus may increase what Fordyce (1976) refers to as the suffering component of the pain experience. Recognizing the importance of emotional and cognitive responses to pain in determining the extent of suffering experienced by pain patients, researchers have developed a variety of measures to assess these responses indirectly. Thus, self-report measures of patient behavior in response to pain evaluate subjective aspects of the pain experience such as negative cognitions (Cognitive Error Questionnaire, Lefebvre 1981; Inventory of Negative Thoughts in Response to Pain, Gil et al. 19901, adaptive and maladaptive thoughts (Pain Cognitions Questionnaire, Boston et al 19901 positive and negative cognitive and overt behavioral pain coping strategies (Coping Strategies Questionnaire (CSQ), Rosenstiel and Keefe 19831, and beliefs and attitudes associated with functional impairment (Pain and Impairment Relationship Scale, Riley et al. 1988; Slater et al. 1991). While these are clearly important dimensions to assess, they do not yield information which directly pertains to pain-related anxiety and which would further our understanding of its role in the chronic pain experience. There has been one attempt to assess fear responses to pain in chronic pain patients. This was a 6-item Fear Self-Statements subscale included in an expanded version of the CSQ (Gil et al. 19891. In their study of patients with pain from sickle cell disease, Gil et al. (1989) found that high scores on a negative thinking and passive adherence coping factor (which included the Fear Self-Statements subscale) predicted greater severity of painful episodes, lower Ievels of activity, more psychological distress, and more frequent health care utiiization. The numerous self-report measures discussed above. including the CSQ Fear Self-Statements subscale of Gil et al. (19891, focus on ~ognitions only. With the exception of the CSQ, which includes behavioral pain coping responses, these commonly used measures de-
vote little or no attention to overt behavioral and physiological responses to pain which are of particular interest in the study of anxiety states. This paper describes the development of a self-report instrument, the Pain Anxiety Symptoms Scale (PASS), to measure fear of pain. This measure is intended to provide a means of evaluating the importance of fear of pain in exaggerated or persistent pain behaviors. As a research tool, it may prove useful for classifying pain patients with respect to their level of pain-related anxiety. This information will, in turn, allow examination of how anxiety responses interact with other factors to enhance the experience of pain. Furthermore, it may facilitate development of individuahzed treatment inte~entions based on the degree to which fear is a component in an individual’s pain experience. Thus, as we gain a better understanding of the role of anxiety in clinical pain, this instrument may have important clinical utility as well. This instrument may also contribute to available measures of pain behavior by broadening the scope of assessment to include physiological and motoric response domains. Consistent with the Three-Systems Model of fear (Lang 1968; Hugdahl 19811, this instrument assesses fear of pain behaviors in 3 response modalities: cognitive, physiologic and motoric. Thus, patients are asked to respond to items which describe (a> fearful thoughts and ruminations about the consequences of their pain, (b) physiological symptoms of fear associated with the experience of pain, and (c> avoidance and escape of activities which they believe may increase pain. Such a tri-modal assessment of fear of pain will facilitate its study within the current framework employed in the study of anxiety disorders. For exampie. it has been shown that individuals who report specific fears (i.e., phobias) often show discordance or desynchrony of response modalities in the expression of their fears (Hodgson and Rachman 1974; Rachman and Hodgson 1974). Similarly, fear of pain may be expressed disproportionately among the 3 response channels, and behaviors of these separate channels may respond differently to inte~entions. If, like other phobias, fear of pain exhibits individual differences in the dominant response channel, the information gleaned from a multimodal assessment may have important implications for treatment of chronic pain problems.
Method Subjects The subjects were 104 outpatients (48 males, 56 females) evaiuated consecutively at a multidiscipljna~ pain management center. Mean age of the sample was 45.0 years (SD. = 13.4). Seventy-five percent of the patients were married, 12% single, 9% divorced. and
69 4% widowed. Mean years of education was 12.0 (SD. = 2.3). The majority of patients presented with back pain (69%), but the sample also included patients with extremity, facial/head, and torso pain complaints. Pain complaints were chronic in nature. All patients reported pain that persisted despite multiple medical interventions. The mean duration of pain was 63.1 months (SD. = 105.8). Forty percent of patients had undergone at least 1 pain-related surgery, and 52% were taking narcotic analgesics on a regular basis. The PASS was administered as part of a comprehensive pain assessment procedure. Patients completed the PASS and other standardized inventories at home several weeks prior to their scheduled appointment in the pain management center. The standardized inventories included commonly employed measures of depression, anxiety, pain, and disability and are described below.
Measures PASS. The initial scale consisted of 62 rationally derived items generated to assess fear of pain in each of the 3 response modes. Items were modeled after items of commonly used anxiety measures and the criterion for item inclusion was a logical rather than empirical relationship with the fear of pain construct. Item content represented anxiety symptoms frequently described in the anxiety disorders literature and patients’ descriptions of their fears related to pain. Items were developed for inclusion in 4 subscales. The 1st subscale, Fear of Pain (19 items), was intended to measure fearful thoughts related to the experience of pain or anticipated negative consequences of pain. The 2nd subscale, Cognitive Anxiety (10 items), was designed to assess cognitive symptoms related to the experience of pain, such as racing thoughts or impaired concentration. The 3rd subscale, Somatic Anxiety (16 items), assessed symptoms reflecting physiological arousal related to the experience of pain. The 4th subscale, Escape and Avoidance (17 items), assessed overt behavioral responses to pain. Table I shows sample items for each of these subscales.
Patients were instructed to rate the frequency of occurrence of each of the 62 behaviors on a 6-point scale from 0 ‘never’ to 5 ‘always’. The total score was computed by reversing 11 negatively keyed items and summing the ratings across the entire measure. Subscale scores were computed by totaling responses to items designated for each subscale. Beck Depression Incwntory (BDI). The BDI (Beck et al. 1961) is a 21-item, self-report measure of depression. It assesses common cognitive and vegetative symptoms of depression. More than 25 years of research evaluating the psychometric properties of the BDI has indicated that it has excellent reliability and validity (Beck et al. 1988). Cognirive Somatic Anxiety Questionnaire (C&IQ). Symptoms of anxiety were assessed with the CSAQ (Schwartz et al. 1978). The CSAQ consists of a list of 14 symptoms of anxiety, including both cognitive and somatic aspects. Respondents are asked to rate the degree to which they experience each of these symptoms when they are anxious. Factor analyses of the CSAQ have identified distinct somatic and cognitive factors (Steptoe and Kearsley 1990). The scale yields separate scores for each of these aspects. Coping Strategies Questionnaire (CSQ). The CSQ (Rosenstiel and Keefe 1983) is a 42-item questionnaire which assesses self-reported use of 7 different cognitive and behavioral pain coping strategies. Only the Catastrophizing subscale was calculated for this study. This ‘6-item scale assesses negative thinking in response to pain. McCiN Pain Questionnaire (MPQ). The MPQ (Melzack 1975) consists of 20 subclasses of 78 adjectives divided among 4 dimensions: sensory, affective, evaluative, and miscellaneous. The purpose of the MPQ is to provide quantitative indices of the subjective pain experience. It has become the most widely used measure of pain and has demonstrated acceptable reliability and face, construct, discriminant, and concurrent validity (Reading 1983). The MPQ yields several variables including scores for each of the separate dimensions and a total score. Mu~tidimensionnl Pain Inventory (MPI). The MPI (formerly the WHYMPI, Kerns et al. 1985) is a brief, comprehensive measure of important aspects of the subjective experience of chronic pain based
TABLE I SAMPLE ITEMS FROM THE PAIN ANXIETY SYMPTOMS SCALE (PASS) Subscale
Item content
Somatic anxiety
I become sweaty when in pain. Pain seems to cause my heart to pound or race. When I sense pain, I feel dizzy or faint. I have pressure or tightness in my chest when in pain. I can stay relaxed when I hurt.
Cognitive Anxiety
I feel disoriented and confused when I hurt. When I hurt, I think about the pain constantly. I am bothered by unwanted thoughts when I’m in pain. My thoughts are agitated and keyed up as pain approaches. During painful episodes it is difficult for me to think of anything besides the pain. I worry when I am in pain.
Fear
I think that pain is a signal that means I am damaging myself. I dread feeling pain. When pain comes on strong, I think that I might become paralyzed or totally disabled. I am afraid that I will have more pain if I am not careful. I think that if my pain gets too severe, it will never decrease.
Escape/Avoidance
When I feel pain I try to stay as still as possible. I try to avoid activities which cause pain. As soon as pain comes on I take medication to reduce it. I seek reassurance that I am OK during times of more severe pain. I go immediately to bed when I feel severe pain.
Note: subjects respond to each item by selecting a frequency rating from 0 ‘never’ to 5 ‘always’.
70 TABLE
II
SUMMARY
STATISTICS
FOR PASS SUBSCALES
AND TOTAL
SCALE
SCORES
Subscale
No. of items
Item means
S.D.
Alpha
I
2
3
Somatic Cognitive Fear Est./Avoid
14 10 14 15
1.73 2.56 2.21 2.54
1.12 1.10 1.04 0.92
0.89 0.87 0.85 0.8 I
0.68 0.64 0.48
0.70 0.5 I
0.45
Total
53
2.24
0.88
0.94
0.85
0.86
0.85
“ All correlations
significant
” 4
0.74
at P < 0.001. N = 104
on the cognitive-behavioral perspective of chronic pain. The 52 items of the MPI divide into 3 major parts, each containing several subscales. The inventory examines the impact of pain on the patient’s life, responses of significant others to the patient’s pain behaviors, and level of participation in typical daily activities. Research with the MPI suggests that it has achieved adequate reliability, validity, and clinical utility (Kerns et al. 1985). Pain Disability Index (PDI). The PDI (Pollard 19841 is a 7-item, self-report measure which assesses patients’ perceived level of disability in 7 life areas. The PDI yields a total score, as well as factor scores for pain-related disability in discretionary and obligatory activities. Recent research has supported the factor structure, validity, and retest reliability of the PDI (Tait et al. 19901 and its construct validity (Jerome and Gross 1991). Spielberger Truit Anxiety Scale (STAI-T). The STAI-T (Spielberger et al. 1970) is a 20-item inventory which assesses individuals’ predisposition to judge situations as dangerous or threatening and to respond with increased levels of state anxiety. The scale is widely used and has been found to have high internal consistency as well as high retest reliability and expected correlations with personality based measures of anxiety such as the Taylor Manifest Anxiety Scale.
TABLE
Intercorrelations
Results Scale development and psychometrics
Preliminary analyses included examination of frequency distributions for item responses and corrected item-scale correlations (correlations of items with their respective scale scores computed with the item omitted). Based on these analyses, 1 item was eliminated because of a highly skewed distribution and 7 items were eliminated because they correlated more highly with a subscale other than the one for which they were written. In these cases, examination of item content indicated that these items were not conceptually similar to the other subscales. A final item was eliminated from further analyses because it was not significantly correlated (at P < 0.05) with any of the PASS subscales. The final inventory submitted to further analyses consisted of 53 items, 14 assessing somatic anxiety,
III
CORRELATIONS
OF
PASS
SUBSCALES
AND
TOTAL
SCORES
WITH
MEASURES
OF
PAIN,
ANXIETY,
DEPRESSION
DISABILITY PASS scores Somatic
Cognitive
Fear
Est./Avoid
Total
CSAQ Cognitive Somatic
0.49 ** 0.74 **
0.61 ** 0.55 * *
0.53 ** 0.56 * *
0.25 0.17
0.54 ** 0.61 **
McGill Sensory Affective STAI-T
0.45 ** 0.51 ** 0.52 **
0.26 * 0.33 ** 0.67 **
0.20 0.36 ** 0.53 **
0. I6 0.31 ** 0.29 *
0.31 ** 0.44 ** 0.60 * *
MPI Pain severity Interference
0.35 ** 0.28 *
0.25 * 0.33 **
0.28 * 0.31 **
0.18 0.36 **
0.32 * * 0.39 **
0.67 0.51 0.39 0.25
0.67 0.67 0.39 0.27
0.66 * * 0.50 ** 0.40 ** 0.19
0.42 ** 0.30 ** 0.30 * * 0.16
0.73 0.57 0.45 0.29
CSQ Catastrophizing BDI PDI Tranquilizer/anxiolytic
use
** ** ** *
Note: * P < 0.01, * * P < 0.001. All probability
** ** ** *
values are l-tailed.
** ** ** *
AND
71
10 assessing cognitive anxiety, 14 assessing fear, and 15 assessing escape and avoidance responses. Table II includes summary statistics for the 4 subscales and the total scale score. Cronbach’s coefficient alpha was computed for each scale demonstrating adequate internal consistency (see Table II). Scale intercorrelations indicate that the subscales significantly intercorrelate. Squaring the interscale correlations reveals that overlapping variance ranges from 0.20 to 0.45, indicating that each scale provides unique information. Construct validity
Construct validity represents the extent to which a test is demonstrated to measure a theoretical construct or non-operationalized variable. One way to provide evidence for construct validity is to examine the correlations of a measure with theoretically related measures. To assess the construct validity of the PASS, the relationships between the various PASS scores and measures of anxiety, pain, and maladaptive coping responses to pain were assessed with Pearson product-moment correlations (see Table III). The validity of the somatic and cognitive anxiety scales of the PASS is supported by higher correlations between reTABLE
spective somatic and cognitive factors of the CSAQ. Significance tests for differences between correlated TS confirmed the statistical significance of these results in comparisons of the correlations of the PASS Cognitive Anxiety and Somatic Anxiety subscales with the CSAQ cognitive factor (t (101) = 1.92; P < 0.05) and the correlations of these PASS subscales with the CSAQ somatic factor (t (101) = 7.61; P < 0.001). All PASS variables demonstrated higher correlations with the affective dimension of the MPQ than with the sensory dimension. Finally, the trait form of the STAI, the pain severity scale of the MPI, and the catastrophizing scale of the CSQ showed consistent significant correlations with PASS subscales, demonstrating predictable overlap between these concepts and the behaviors assessed on the PASS (see Table III). Concurrent validity
While construct validity involves theoretical considerations, it also is important to demonstrate the practical or criterion-related validity of a measure. In the case of the PASS, criterion-related validity can be assessed by examining correlations of the PASS subscales with patient outcome variables that it should
IV
RESULTS OF HIERARCHICAL REGRESSION ANALYSES EMPLOYING DISTRESS IN ADDITION TO THE PASS TOTAL SCORE AS PREDICTORS ENCE DUE TO PAIN (MPI) Dependent Step Interference Equation
variable
R2
Beta
COMMON MEASURE OF PAIN AND PSYCHOLOGICAL OF SELF-RATED DISABILITY (PDI), AND INTERFER-
St.2
Fchange
Probability
1 0.23 0.24
0.38 0.17
0.096 0.019
27.43 2.36
0.0000 0.12
STAI-T PASS Equation 3
0.11 0.17
0.17 0.28
0.018 0.052
11.54 5.46
0.001 0.02
MPQ sensory PASS Equation 4
0.008 0.15
- 0.030 0.39
0.0008 0.14
0.82 15.39
0.37 0.0002
0.18 0.25
0.33 0.28
0.10 0.070
20.47 8.76
0.0000 0.004
0.18 0.24
0.23 0.32
0.035 0.068
19.32 8.41
0.0000 0.005
STAI-T PASS Equation 3
0.12 0.21
0.11 0.38
0.008 0.094
11.70 10.44
0.0009 0.002
MPQ sensory PASS Equation 4
0.03 0.20
0.04 0.44
0.0015 0.17
3.03 20.39
0.085 0.0000
0.25 0.34
0.40 0.32
0.14 0.095
31.51 13.60
0.0000 0.0004
BDI PASS Equation
2
Pain severity PASS Disability Equation BDI PASS Equation
1
2
Pain severity PASS
72
predict. When criterion-related validity is evaluated by correlating measures administered at one point in time, this type of validity is referred to as concurrent. Concurrent validity for the PASS was assessed by examining the relationships between the PASS scores and common measures of disability and depression. Correlational analyses indicated that PASS scores related significantly to scores from the interference scale of the MPI, scores from the BDI, and self-rated disability as measured by the PDI. In addition, point biserial correlations between PASS scores and a dichotomous variable representing use of tranquilizing or anxiolytic medications indicated that the Somatic and Cognitive Anxiety subscales as well as the total score were positively related to use of these medications (see Table III). Next, a series of hierarchical multiple regression analyses were performed. These assessed the significance of the unique increment in variance accounted for by the PASS in the prediction of disability after controlling for various measures of pain and psychological distress. Dependent variables were the PDI total score and the interference scale of the MPI. Independent variables entered into the equations before testing for the contribution of the PASS included the MPQ sensory score, the MPI pain severity scale score, the BDI score, and the STAI-T score. Results are included in Table IV. With one exception the PASS scores significantly contributed to the prediction of disability and interference due to pain after controling for variance related to the other predictors. The squared semi-partial correlation coefficients indicate that, in those equations in which the PASS contributed significantly, it accounted for a unique portion of variance which ranged from 5.2% to 17%. It consistently accounted for more unique outcome variance than the STAI or the sensory dimension of the MPQ.
Discussion
Preliminary analyses support the reliability and validity of the PASS as a measure of pain-related fear and anxiety. High alpha coefficients suggest that the PASS and its subscales demonstrate good internal consistency. Interscale correlations demonstrate that subscales are meaningfully related but also provide independent information about fear and anxiety responses. Construct validity of the PASS was supported by moderate correlations with other measures of anxiety. Moreover, although 4 of 5 variables from the PASS correlate with the CSAQ factors at a moderate to high moderate level, results support a differential relationship between the Cognitive and Somatic subscales of the PASS and the respective cognitive and somatic factors of the CSAQ. This finding supports the con-
struct validity of these PASS subscales. All subscales and the total PASS score showed higher correlations with the MPQ affective dimension than with the MPQ sensory dimension, indicating that fear related to pain is not simply a function of the sensory experience of pain. The results also confirm the concurrent validity of the PASS in relation to measures of disability, depression, and medication use, all pervasive consequences of chronic pain. Correlation analyses revealed that painrelated fear and anxiety, as measured by the PASS, are significant predictors of disability and interference with daily activities due to pain. Regression analyses controlling for measures of pain and psychological distress revealed that, with one exception, the PASS made a significant unique contribution to the prediction of disability. The PASS was a much better predictor of disability and interference than the Sensory subscale of the MPQ. The PASS also proved to be a better predictor of disability and interference than a measure of general anxiety (STAI-T). Relative to a measure of emotional distress, i.e., the BDI, the PASS made a greater contribution to the prediction of disability but added little to the prediction of interference. Overall, these results suggest that the PASS predicts important patient outcomes and provides information which is not currently available from other commonly used measures. The validity results discussed above include a large number of significance tests, implying a possibly unacceptable level of chance findings. Three points are relevant to understand better this limitation of the data. First, variables from the PASS demonstrate consistent patterns of relations with other variables, suggesting that chance does not play an important role in the results. For example, both the CSAQ and the STAI-T are measures of trait anxiety. Although item content of these measures is different, both measures demonstrated similar relations with the PASS increasing confidence in these findings. Likewise, similarities between the variables assessed by the MPI Interference subscale and the PDI, and by the MPI Pain Severity subscale and the MPQ sensory factor, tend to increase our confidence in the correlational results. Second, examination of the probability values associated with most of our results reveals the majority of the results attain low probability values. Third, to help reduce reliance on possibly spurious results, a more conservative significance criterion was chosen for Table III. Overall, the findings discussed above suggest that fear of pain can be conceptualized as a multidimensional response which may contribute significantly to the chronic pain experience. Further investigations of the psychometric properties of the PASS should seek to establish the temporal stability of the measure, as
73
well as the behavioral validity of the Somatic and Escape/Avoidance subscales. For example, it will be important to demonstrate that high scores on these subscales are highly correlated with the physiological measures of arousal in response to pain, with clinical observations, and spouse reports of escape and avoidance behaviors. This latter point is crucial since the validity data presented here only include intercorrelations of self-report instruments. Shared variance related to the method of data collection may contribute to these correlations. Finally, factor analyses should be conducted in order to establish the factor structure of the PASS and its concordance with the intended subscales. Creating subscales with greater discriminant validity also would be valuable. Scale overlap, particularly between the Fear and Cognitive Anxiety subscales, may be reduced by examining factor results and further examining item-scale correlations to eliminate items that reduce subscale independence. The purpose of this instrument is to facilitate the study of pain-related fear and anxiety in chronic pain populations with the goal of improving treatment outcome. The PASS may be particularly useful in this respect if it enables clinicians to identify empirical subtypes of pain patients who may respond differentially to treatment interventions. For example, it is conceivable that individuals whose fear of pain is manifested primarily in the physiological response system may be more responsive to relaxation training than to attempts at cognitive restructuring. In order to determine whether the PASS is useful in distinguishing subgroups of patients, cluster analyses of the PASS on a broader sample of chronic pain patients are currently being conducted. References Al Absi, M. and Rokke, P.D., Can anxiety help us tolerate pain?, Pain, 46 (1991) 43-51. Arntz, A., Dreessen, L. and Merckelbach, H., Attention, not anxiety, influences pain, Behav. Res. Ther., 29 (1991) 41-50. Beck, A.T., Steer, R.A. and Garbin, M.G., Psychometric properties of the Beck Depression Inventory: twenty-five years of evaluation, Clin. Psychol. Rev., 8 (1988) 77-100. Beck, A.T., Ward, C.H., Mendelson, M., Mock, J. and Erbaugh, J., An inventory for measuring depression, Arch. Gen. Psych., 4 (1961) 561-571. Bobey, M.J. and Davidson, P.O., Psychological factors affecting pain tolerance, J. Psychosom. Res., 14 (1970) 371-376. Boston, K., Pearce, S.A. and Richardson, P.H., The Pain Cognitions Questionnaire, J. Psychosom. Res., 34 (1990) 103-109. Cornwall, A. and Donderi, D.C., The effect of experimentally induced anxiety on the experience of pressure pain, Pain, 35 (1988) 105-113. Fordyce, W.E., Behavioral Methods in Chronic Pain and Illness, C.V. Mosby, St. Louis, MO, 1976, 236 pp.
Gil, K.M., Abrams, M.R., Phillips, G. and Keefe, F.J., Sickle cell disease pain: relation of coping strategies to adjustment, J. Consult. Clin. Psychol., 57 (1989) 725-731. Gil, K.M., Williams, D.A., Keefe, F.J. and Beckham, J.C., The relationship of negative thoughts to pain and psychological distress, Behav. Ther., 21 (1990) 349-362. Hodgson, R. and Rachman, S., Desynchrony in measures of fear, Behav. Res. Ther., 12 (1974) 319-326. Hugdahl, K., The three-system model of fear and emotion: a critical examination, Behav. Res. Ther., 19 (1981) 75-85. Jerome, A. and Gross, R.T., Pain Disability Index: construct and discriminant validity, Arch. Phys. Med. Rehab., 72 (1991) 920-922. Kerns, R.D., Turk, D.C. and Rudy, T.E., The West Haven-Yale Multidimensional Pain Inventory (WHYMPI), Pain, 23 (1985) 345-356. Lang, P.J., Fear reduction and fear behavior: problems in treating a construct. In: J.M. Shilen (Ed.), Research in Psychotherapy, Vol. 3, American Psychological Association, Washington, DC, 1968, pp. 90-103. Lefebvre, M.F., Cognitive distortion and cognitive errors in depressed psychiatric and low back pain patients, J. Consult. Clin. Psychol., 49 (1981) 517-525. Lethem, J., Slade, P.D., Troup, J.D.G. and Bentley, G., Outline of a fear-avoidance model of exaggerated pain perception-I, Behav. Res. Ther., 21 (1983) 401-408. Melzack, R., The McGill Pain Questionnaire: major properties and scoring methods, Pain, 1 (1975) 277-299. Phillips, H.C., Avoidance behavior and its role in sustaining chronic pain, Behav. Res. Ther., 25 (1987) 273-279. Phillips, H.C. and Jahanshahi, M., Chronic pain: an experimental analysis of the effects of exposure, Behav. Res. Ther., 23 (1985) 281-290. Pollard, C.A., Preliminary validity study Pain Disability Index, Percept. Motor Skills, 59 (1984) 974. Rachman, S. and Hodgson, R., Synchrony and desynchrony in fear and avoidance, Behav. Res. Ther., 12 (1974) 311-318. Reading, A.E., The McGill Pain Questionnaire: an appraisal. In: R. Melzack (Ed.), Pain Measurement and Assessment, Raven Press, New York, 1983, pp. 55-61. Riley, J.F., Ahern, D.K. and Follick, M.J., Chronic pain and functional impairment: assessing beliefs about their relationship, Arch. Phys. Med. Rehab., 69 (1988) 579-582. Rosenstiel, A.K. and Keefe, F.J., The use of coping strategies in low back pain patients: relationship to patient characteristics and current adjustment, Pain, 17 (1983) 33-40. Schwartz, G.E., Davidson, R.J. and Goleman, D.J., Patterning of cognitive and somatic processes in the self-regulation of anxiety: effects of meditation versus exercise, Psychosom. Med., 40 (1978) 321-328. Slater, M.A., Hall, H.F., Atkinson, H. and Garfin, S.R., Pain and impairment beliefs in chronic low back pain: validation of the Pain and Impairment Relationship Scale (PAIRS), Pain, 44 (1991) 51-56. Spielberger, C.D., Gorsuch, R.L. and Lushene, R.E., Manual for the State-Trait Anxiety Inventory, Consulting Psychologist Press, Palo Alto, CA, 1970. Steptoe, A. and Kearsley, N., Cognitive and somatic anxiety, Behav. Res. Ther., 28 (1990) 75-81. Tait, R.C., Chibnall, J.T. and Krause, S., The Pain Disability Index: psychometric properties, Pain, 40 (1990) 171-182. Wall, P.D., On the relation of injury to pain, Pain, 6 (1979) 253-264. Weisenberg, M., Aviram, O., Wolf, Y. and Raphaeli, N., Relevant and irrelevant anxiety in the reaction to pain, Pain, 20 (1984) 371-383.
