Journal of Traumatic Stress December 2014, 27, 721–724
BRIEF REPORT
Does Guilt Mediate the Association Between Tonic Immobility and Posttraumatic Stress Disorder Symptoms in Female Trauma Survivors? Michelle J. Bovin,1,2 Thomas S. Dodson,1 Brian N. Smith,1,2 Kristin Gregor,1,2 Brian P. Marx,1,2 and Suzanne L. Pineles1,2 1
2
National Center for PTSD, VA Boston Healthcare System, Boston, Massachusetts, USA Department of Psychiatry, Boston University School of Medicine, Boston, Massachusetts, USA
Tonic immobility (TI) is an involuntary freezing response that can occur during a traumatic event. TI has been identified as a risk factor for posttraumatic stress disorder (PTSD), although the mechanism for this relationship remains unclear. This study evaluated a particular possible mechanism for the relationship between TI and PTSD symptoms: posttraumatic guilt. To examine this possibility, we assessed 63 female trauma survivors for TI, posttraumatic guilt, and PTSD symptom severity. As expected, the role of guilt in the association between TI and PTSD symptom severity was consistent with mediation (B = 0.35; p < .05). Thus, guilt may be an important mechanism by which trauma survivors who experience TI later develop PTSD symptoms. We discuss the clinical implications, including the importance of educating those who experienced TI during their trauma about the involuntary nature of this experience.
Results of research have suggested that, like nonhuman animals, humans may experience tonic immobility (TI), an involuntary, reflexive state characterized by physical immobility, muscular rigidity, and suppressed vocal behavior, when confronted with inescapable and fear-inducing situations (Marx, Forsyth, Gallup, Fus´e, & Lexington, 2008). Although TI was first identified in humans during sexual assault (Russell, 1974), studies have found that survivors of other types of trauma (e.g., physical assault, natural disasters; Abrams, Carleton, Taylor, & Asmundson, 2009) may also experience TI. TI has been associated with posttraumatic stress disorder (PTSD) and other posttrauma difficulties (Abrams et al., 2009). Although a causal mechanism has not been identified, one possibility is guilt—a negative evaluation of an action either taken or not taken. During TI, the individual remains cognitively alert,
but unable to respond defensively. Without understanding TI, these individuals may feel guilt for their inaction. In fact, some data show that individuals who behave passively peritraumatically are more likely to experience guilt and self-blame than those who behave actively (Lee, Scragg, & Turner, 2001; Mezey & Taylor, 1988). No study, of which we are aware, has directly tested the role of guilt in the relationship between TI and PTSD symptoms. In the current study, we examined the associations among TI, guilt, and PTSD symptoms in a sample of trauma-exposed women. We hypothesized that guilt would mediate the association between TI and PTSD symptom severity. Method Participants and Procedure From a sample of female trauma survivors, 63 who participated in a screening session for a larger investigation examining menstrual-phase effects on PTSD psychophysiology and who completed a measure assessing TI (that was added after the larger study began) were included in this study. Exclusion criteria were past 30-day drug use/heavy alcohol use, current infectious illnesses, history of organic brain disorder, schizophrenia, use of psychotropic medications in the past 4 weeks, irregular menstrual cycle, oral contraceptive use, and peri- or postmenopausal status. All participants provided informed consent
Support for this work was provided by a Veterans Affairs Career Development Award (Principal Investigator: Pineles) from the Clinical Sciences Research and Development Service, Department of Veterans Affairs. Correspondence concerning this article should be addressed to Michelle J. Bovin, Women’s Health Sciences Division (116B-3), National Center for PTSD, VA Boston Healthcare System, 150 South Huntington Avenue, Boston, MA 02130. E-mail: [email protected] Published 2014. This article is a US Government work and is in the public domain in the USA. View this article online at wileyonlinelibrary.com DOI: 10.1002/jts.21963
721
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Bovin et al.
prior to participation, and institutional review board approval at the VA Boston Healthcare System was secured. Participants in the current study ranged in age from 19 to 52 years (M = 34.48 years, SD = 9.89) and were ethnically diverse (47.6% African American; 27.0% Caucasian; 12.7% Asian American; 7.9% Hispanic; 1.6% American Indian; 3.2% self-reported as Other). Participants endorsed experiencing a range of traumatic events, including childhood sexual/physical abuse (68.3%), adult sexual/physical abuse (52.4%), motor vehicle accidents (36.5%), another life-threatening event (82.5%), witnessing or learning about death (79.4%), and being stalked (33.3%). Based on the Clinician-Administered PTSD Scale for DSM-IV (CAPS-IV; Blake et al., 1995) Frequency ࣙ 1/Intensity ࣙ 2 rule (Weathers, Ruscio, & Keane, 1999), 52.4% of the sample met criteria for current PTSD. Based on the Structured Clinical Interview for DSM-IV (SCID; First, Spitzer, Williams, & Gibbon, 2000), participants in the study had a range of psychiatric comorbidities, including panic disorder (9.7%), simple phobia (22.6%), social phobia (17.7%), obsessive compulsive disorder (5.0%), generalized anxiety disorder (14.5%), major depressive disorder (17.2%), dysthymia (3.3%), somatoform disorders (6.5%), and eating disorders (6.3%). Measures The self-report Traumatic Life Events Questionnaire (TLEQ; Kubany et al., 2000) assessed exposure to 22 PTSD Criterion A events according to the Diagnostic and Statistical Manual of Mental Disorders (4th ed., DSM-IV; American Psychiatric Association, 1994). Each event is scored on a 7-point scale ranging from 0 = never to 6 = more than five times; if the event is endorsed, the participant is then asked “Did you experience intense fear, helplessness, or horror when it happened?” (yes/no). The scale has demonstrated good psychometric properties (Kubany et al., 2000). A modified version of the Tonic Immobility Scale-Adult Version (TIS-A; Forsyth, Marx, Fus´e, Heidt, & Gallup, 2000) assessed TI. The TIS-A is a two-part, 30-item questionnaire developed to measure both TI and emotions and behaviors thought to covary with TI during an adult sexual assault episode. In the current study, a modified version was used that applied to a range of traumatic events. Part 1 of the TIS-A contains 12 items that assess dimensional aspects of TI and its antecedents. Factor analyses indicate that Part 1 of the TIS-A consists of two factors: a TI factor and a peritraumatic fear factor (Fus´e, Forsyth, Marx, Gallup, & Weaver, 2007). Part 2 of the TIS-A contains 17 items that assess behaviors known to covary with TI and hypothesized emotional reactions to the event. In the current study, only the TI factor was used. The TI factor consists of seven questions that assess both the inability of the individual to move during the trauma and factors related to the TI experience. Each item is rated on a 7-point scale, with higher scores indicating higher levels of TI (in the current study the range = 0–42 and α = .63). The CAPS-IV (Blake et al., 1995) is a reliable and valid structured diagnostic interview that assesses PTSD diagnosis
and severity (Weathers, Keane, & Davidson, 2001). For each of the 17 symptoms, a clinician rates two dimensions on separate 5-point scales; these scales are combined across items to form a total PTSD severity score, which was used in this study (α = .94). In the current study, the CAPS was anchored to all the reported DSM-IV PTSD Criterion A events, and not to a specific index event, reported by the participants on the TLEQ. The principal investigator conducted all diagnostic interviews, and presented each at consensus meetings. For the current study, 10% of the interviews were coded by a second rater and interrater reliability was excellent (κ = 1.00). Posttraumatic guilt was assessed using one item from the CAPS-IV associated features section. Participants responded to the question, “Have you felt guilty about anything you did or didn’t do during (EVENT)?” Responses are scored using the same methods as for PTSD severity, with higher scores indicating greater perceptions of guilt. Comorbidity within the sample was determined by the SCID (First et al., 2000), a comprehensive, structured interview that assesses all major Axis I disorders. The interrater reliability (presence vs. absence of comorbid diagnoses) for the SCID was also excellent (κ = 1.00). Data Analysis Prior to conducting analyses to test our hypothesis, bivariate correlations were conducted to examine the associations among the independent variable, dependent variable, and proposed mediator. Next, regression-based models that applied bootstrapping were used to test the consistency with mediation. The significance of hypothesized pathways was tested directly using the PROCESS macro for SPSS version 21 (Hayes, 2013). PROCESS uses listwise deletion to handle missing data (for analyses, effective n = 63). To test the indirect effect, a two-sided 95% bias-corrected confidence interval (CI) was calculated on the basis of 5,000 bootstrap samples. In the model, Path A indicates the association between the independent variable and the mediator, Path B indicates the association between the mediator and the dependent variable, Path C represents the association between the independent and dependent variable without the inclusion of the mediator, and Path C’ represents the relation between the independent and dependent variable after accounting for the effect of the mediator. When CIs of the indirect effect of a mediator do not include 0, the effect is considered statistically significant (Preacher & Hayes, 2008). See Figure 1 for a graphic representation of the tested model. Finally, three additional mediation analyses were conducted using the symptom severity of each of the DSM-IV PTSD symptom clusters (reexperiencing, avoidance/numbing, and hyperarousal) as separate outcome variables. Results In our sample, TI scores ranged from 3 to 36 (M = 22.96, SD = 8.21), guilt scores ranged from 0 to 8 (M = 1.30, SD = 2.27),
Journal of Traumatic Stress DOI 10.1002/jts. Published on behalf of the International Society for Traumatic Stress Studies.
723
Tonic Immobility, Guilt, and PTSD
A Tonic immobility
Path C B = 1.25**, SE = 0.35
PTSD symptom severity
B Path A
Guilt
B = 0.07*, SE = 0.03
Tonic immobility
Path B B = 5.47**, SE = 1.35
Path C’ B = 0.89**, SE = 0.33
PTSD symptom severity
Figure 1. Graphic representation of the mediation model. (A) Tonic immobility affects posttraumatic stress disorder (PTSD) symptom severity. (B) Tonic immobility exerts effects on PTSD symptom severity through guilt. *p < .05. **p < .01.
and PTSD severity scores ranged from 0 to 125 (M = 37.52, SD = 28.32). Bivariate correlations indicated that all variables were significantly correlated (rs ranged from .25 to .52; all ps < .05). As hypothesized, the results of the regression-based model examining the role of guilt in the association between TI and PTSD symptom severity provided evidence consistent with mediation, F(2, 60) = 15.96, R2 = .34, B = 0.35, standard error = 0.14, bootstrapped 95% CI of indirect effects [0.10, 0.66] (see Fig. 1). The percentage of the total effect due to the indirect effect was 28%. Findings from the three additional models using the PTSD symptom clusters as the dependent variables were also consistent with mediation. Specifically, for the reexperiencing cluster, bootstrapped 95% CI of indirect effects was [0.02, 0.28]; for the avoidance/numbing cluster it was [0.04, 0.33]; and for the arousal cluster [0.02, 0.20]. All Fs exceeded 8.00, all R2 s > .21, all Bs > 0.07.
if clinicians can help their patients understand that the nature of TI dictates that they cannot fight back (vs. choosing not to fight back), it may help these patients reduce self-blaming cognitions and PTSD symptoms. This possibility awaits empirical testing. The current study is not without limitations. The use of a cross-sectional design prohibited the determination of causal relationships. The study was also limited by a modest sample size. A larger sample would provide further confidence in these results, and would allow for examination of whether these relationships vary as a function of other factors (e.g., trauma type). In addition, it would allow for determination of whether TI is associated with other forms of psychopathology (e.g., depression, alcohol abuse) and whether guilt also mediates these associations. Another limitation is that the study only included female participants and had a large number of exclusion criteria, both of which limit generalizability. In addition, we used a single item to measure posttraumatic guilt, which may not have fully captured this construct. The fact that this item (which served as our mediator) was part of the same interview as our outcome variable (PTSD symptoms) introduces the possibility that common method effects may have influenced the results. Future studies should examine this question using a more robust measure of guilt. Our model was also vulnerable to the problem of omitted variables because the mediator was not randomly assigned. Further, we were unable to examine whether time since the index event influenced results because PTSD symptoms were assessed in relation to all Criterion A events experienced, rather than in relation to one index event. Finally, like most studies examining peritraumatic variables, the possibility of response and memory biases may have impacted report of TI. Our findings suggest that guilt may be one mechanism by which trauma survivors who experience TI during their traumas later develop PTSD symptoms. It is possible that by educating these individuals about TI and thereby challenging inappropriate beliefs about self-blame, therapists will be able to decrease guilt and subsequently reduce PTSD symptom severity.
Discussion Our results suggest that the role of guilt in the association between TI and PTSD severity is consistent with mediation. TI among humans is a relatively newly studied area, and this is the first study to demonstrate guilt as a potential mechanism linking TI and PTSD symptoms. Our findings are consistent with literature suggesting that passivity during a trauma is associated with guilt (e.g., Lee et al., 2001), and with findings that guilt is associated with PTSD (e.g., Henning & Frueh, 1997). These results highlight the importance of educating individuals who have experienced TI and subsequently develop PTSD symptoms. Education about the involuntary nature of TI may reduce guilt about peritraumatic behavioral passivity, which may in turn reduce PTSD symptoms. Further, clinicians may be able to use this information to challenge their patients’ negative cognitions about their role during the trauma. For example,
References Abrams, M. P., Carleton, R., Taylor, S., & Asmundson, G. G. (2009). Human tonic immobility: Measurement and correlates. Depression and Anxiety, 26, 550–556. doi:10.1002/da.20462 American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: Author. Blake, D. D., Weathers, F. W., Nagy, L. M., Kaloupek, D. G., Gusman, F. D., Charney, D. S., & Keane, T. M. (1995). The development of a clinician-administered PTSD scale. Journal of Traumatic Stress, 8, 75–90. doi:10.1002/jts.2490080106 First, M., Spitzer, R., Williams, J., & Gibbon, M. (2000). Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I). In American Psychiatric Association (Ed.), Handbook of psychiatric measures (pp. 49–53). Washington, DC: American Psychiatric Association. Forsyth, J. P., Marx, B., Fus´e, T. M. K., Heidt, J., & Gallup, G. G., Jr. (2000). The Tonic Immobility Scale–Adult Form. Albany, NY: Author.
Journal of Traumatic Stress DOI 10.1002/jts. Published on behalf of the International Society for Traumatic Stress Studies.
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Fus´e, T., Forsyth, J. P., Marx, B., Gallup, G. G., & Weaver, S. (2007). Factor structure of the Tonic Immobility Scale in female sexual assault survivors: An exploratory and confirmatory factor analysis. Journal of Anxiety Disorders, 21, 265–283. doi:10.1016/j.janxdis.2006.05.004
Marx, B. P., Forsyth, J. P., Gallup, G. G., Fus´e, T., & Lexington, J. M. (2008). Tonic immobility as an evolved predator defense: Implications for sexual assault survivors. Clinical Psychology: Science and Practice, 15, 74–90. doi:10.1111/j.1468-2850.2008.00112.x
Hayes, A. F. (2013). Introduction to mediation, moderation, and conditional process analysis: A regression-based approach. New York, NY: Guilford Press.
Mezey, G. C., & Taylor, P. J. (1988). Psychological reactions of women who have been raped: A descriptive and comparative study. The British Journal of Psychiatry, 152, 330–339. doi:10.1192/bjp.152.3.330
Henning, K. R., & Frueh, B. C. (1997). Combat guilt and its relationship to PTSD symptoms. Journal of Clinical Psychology, 53, 801–808. doi:10.1002/(SICI)1097-4679(199712)53:83.3.CO;2-V
Preacher, K. J., & Hayes, A. F. (2008). Asymptotic and resampling strategies for assessing and comparing indirect effects in multiple mediator models. Behavior Research Methods, 40, 879–891. doi:10.3758/BRM.40.3.879
Kubany, E. S., Leisen, M. B., Kaplan, A. S., Watson, S. B., Haynes, S. N., Owens, J. A., & Burns, K. (2000). Development and preliminary validation of a brief broad-spectrum measure of trauma-exposure: The Traumatic Life Events Questionnaire. Psychological Assessment, 12, 210–224. doi:10.1037/1040-3590.12.2.210
Russell, D. E. H. (1974). The politics of rape: The victim’s perspective. New York, NY: Stein & Day.
Lee, D. A., Scragg, P., & Turner, S. (2001). The role of shame and guilt in traumatic events: A clinical model of shame-based and guilt based PTSD. British Journal of Medical Psychology, 74, 451–466. doi:10.1348/000711201161109
Weathers, F. W., Keane, T., & Davidson, J. (2001). Clinician-Administered PTSD Scale: A review of the first ten years of research. Depression and Anxiety, 13, 132–156. doi:10.1002/da.1029 Weathers, F. W., Ruscio, A. M., & Keane, T. M. (1999). Psychometric properties of nine scoring rules for the Clinician-Administered Posttraumatic Stress Disorder Scale. Psychological Assessment, 11, 124–133. doi:10.1037/10403590.11.2.124
Journal of Traumatic Stress DOI 10.1002/jts. Published on behalf of the International Society for Traumatic Stress Studies.
BRIEF REPORT
Does Guilt Mediate the Association Between Tonic Immobility and Posttraumatic Stress Disorder Symptoms in Female Trauma Survivors? Michelle J. Bovin,1,2 Thomas S. Dodson,1 Brian N. Smith,1,2 Kristin Gregor,1,2 Brian P. Marx,1,2 and Suzanne L. Pineles1,2 1
2
National Center for PTSD, VA Boston Healthcare System, Boston, Massachusetts, USA Department of Psychiatry, Boston University School of Medicine, Boston, Massachusetts, USA
Tonic immobility (TI) is an involuntary freezing response that can occur during a traumatic event. TI has been identified as a risk factor for posttraumatic stress disorder (PTSD), although the mechanism for this relationship remains unclear. This study evaluated a particular possible mechanism for the relationship between TI and PTSD symptoms: posttraumatic guilt. To examine this possibility, we assessed 63 female trauma survivors for TI, posttraumatic guilt, and PTSD symptom severity. As expected, the role of guilt in the association between TI and PTSD symptom severity was consistent with mediation (B = 0.35; p < .05). Thus, guilt may be an important mechanism by which trauma survivors who experience TI later develop PTSD symptoms. We discuss the clinical implications, including the importance of educating those who experienced TI during their trauma about the involuntary nature of this experience.
Results of research have suggested that, like nonhuman animals, humans may experience tonic immobility (TI), an involuntary, reflexive state characterized by physical immobility, muscular rigidity, and suppressed vocal behavior, when confronted with inescapable and fear-inducing situations (Marx, Forsyth, Gallup, Fus´e, & Lexington, 2008). Although TI was first identified in humans during sexual assault (Russell, 1974), studies have found that survivors of other types of trauma (e.g., physical assault, natural disasters; Abrams, Carleton, Taylor, & Asmundson, 2009) may also experience TI. TI has been associated with posttraumatic stress disorder (PTSD) and other posttrauma difficulties (Abrams et al., 2009). Although a causal mechanism has not been identified, one possibility is guilt—a negative evaluation of an action either taken or not taken. During TI, the individual remains cognitively alert,
but unable to respond defensively. Without understanding TI, these individuals may feel guilt for their inaction. In fact, some data show that individuals who behave passively peritraumatically are more likely to experience guilt and self-blame than those who behave actively (Lee, Scragg, & Turner, 2001; Mezey & Taylor, 1988). No study, of which we are aware, has directly tested the role of guilt in the relationship between TI and PTSD symptoms. In the current study, we examined the associations among TI, guilt, and PTSD symptoms in a sample of trauma-exposed women. We hypothesized that guilt would mediate the association between TI and PTSD symptom severity. Method Participants and Procedure From a sample of female trauma survivors, 63 who participated in a screening session for a larger investigation examining menstrual-phase effects on PTSD psychophysiology and who completed a measure assessing TI (that was added after the larger study began) were included in this study. Exclusion criteria were past 30-day drug use/heavy alcohol use, current infectious illnesses, history of organic brain disorder, schizophrenia, use of psychotropic medications in the past 4 weeks, irregular menstrual cycle, oral contraceptive use, and peri- or postmenopausal status. All participants provided informed consent
Support for this work was provided by a Veterans Affairs Career Development Award (Principal Investigator: Pineles) from the Clinical Sciences Research and Development Service, Department of Veterans Affairs. Correspondence concerning this article should be addressed to Michelle J. Bovin, Women’s Health Sciences Division (116B-3), National Center for PTSD, VA Boston Healthcare System, 150 South Huntington Avenue, Boston, MA 02130. E-mail: [email protected] Published 2014. This article is a US Government work and is in the public domain in the USA. View this article online at wileyonlinelibrary.com DOI: 10.1002/jts.21963
721
722
Bovin et al.
prior to participation, and institutional review board approval at the VA Boston Healthcare System was secured. Participants in the current study ranged in age from 19 to 52 years (M = 34.48 years, SD = 9.89) and were ethnically diverse (47.6% African American; 27.0% Caucasian; 12.7% Asian American; 7.9% Hispanic; 1.6% American Indian; 3.2% self-reported as Other). Participants endorsed experiencing a range of traumatic events, including childhood sexual/physical abuse (68.3%), adult sexual/physical abuse (52.4%), motor vehicle accidents (36.5%), another life-threatening event (82.5%), witnessing or learning about death (79.4%), and being stalked (33.3%). Based on the Clinician-Administered PTSD Scale for DSM-IV (CAPS-IV; Blake et al., 1995) Frequency ࣙ 1/Intensity ࣙ 2 rule (Weathers, Ruscio, & Keane, 1999), 52.4% of the sample met criteria for current PTSD. Based on the Structured Clinical Interview for DSM-IV (SCID; First, Spitzer, Williams, & Gibbon, 2000), participants in the study had a range of psychiatric comorbidities, including panic disorder (9.7%), simple phobia (22.6%), social phobia (17.7%), obsessive compulsive disorder (5.0%), generalized anxiety disorder (14.5%), major depressive disorder (17.2%), dysthymia (3.3%), somatoform disorders (6.5%), and eating disorders (6.3%). Measures The self-report Traumatic Life Events Questionnaire (TLEQ; Kubany et al., 2000) assessed exposure to 22 PTSD Criterion A events according to the Diagnostic and Statistical Manual of Mental Disorders (4th ed., DSM-IV; American Psychiatric Association, 1994). Each event is scored on a 7-point scale ranging from 0 = never to 6 = more than five times; if the event is endorsed, the participant is then asked “Did you experience intense fear, helplessness, or horror when it happened?” (yes/no). The scale has demonstrated good psychometric properties (Kubany et al., 2000). A modified version of the Tonic Immobility Scale-Adult Version (TIS-A; Forsyth, Marx, Fus´e, Heidt, & Gallup, 2000) assessed TI. The TIS-A is a two-part, 30-item questionnaire developed to measure both TI and emotions and behaviors thought to covary with TI during an adult sexual assault episode. In the current study, a modified version was used that applied to a range of traumatic events. Part 1 of the TIS-A contains 12 items that assess dimensional aspects of TI and its antecedents. Factor analyses indicate that Part 1 of the TIS-A consists of two factors: a TI factor and a peritraumatic fear factor (Fus´e, Forsyth, Marx, Gallup, & Weaver, 2007). Part 2 of the TIS-A contains 17 items that assess behaviors known to covary with TI and hypothesized emotional reactions to the event. In the current study, only the TI factor was used. The TI factor consists of seven questions that assess both the inability of the individual to move during the trauma and factors related to the TI experience. Each item is rated on a 7-point scale, with higher scores indicating higher levels of TI (in the current study the range = 0–42 and α = .63). The CAPS-IV (Blake et al., 1995) is a reliable and valid structured diagnostic interview that assesses PTSD diagnosis
and severity (Weathers, Keane, & Davidson, 2001). For each of the 17 symptoms, a clinician rates two dimensions on separate 5-point scales; these scales are combined across items to form a total PTSD severity score, which was used in this study (α = .94). In the current study, the CAPS was anchored to all the reported DSM-IV PTSD Criterion A events, and not to a specific index event, reported by the participants on the TLEQ. The principal investigator conducted all diagnostic interviews, and presented each at consensus meetings. For the current study, 10% of the interviews were coded by a second rater and interrater reliability was excellent (κ = 1.00). Posttraumatic guilt was assessed using one item from the CAPS-IV associated features section. Participants responded to the question, “Have you felt guilty about anything you did or didn’t do during (EVENT)?” Responses are scored using the same methods as for PTSD severity, with higher scores indicating greater perceptions of guilt. Comorbidity within the sample was determined by the SCID (First et al., 2000), a comprehensive, structured interview that assesses all major Axis I disorders. The interrater reliability (presence vs. absence of comorbid diagnoses) for the SCID was also excellent (κ = 1.00). Data Analysis Prior to conducting analyses to test our hypothesis, bivariate correlations were conducted to examine the associations among the independent variable, dependent variable, and proposed mediator. Next, regression-based models that applied bootstrapping were used to test the consistency with mediation. The significance of hypothesized pathways was tested directly using the PROCESS macro for SPSS version 21 (Hayes, 2013). PROCESS uses listwise deletion to handle missing data (for analyses, effective n = 63). To test the indirect effect, a two-sided 95% bias-corrected confidence interval (CI) was calculated on the basis of 5,000 bootstrap samples. In the model, Path A indicates the association between the independent variable and the mediator, Path B indicates the association between the mediator and the dependent variable, Path C represents the association between the independent and dependent variable without the inclusion of the mediator, and Path C’ represents the relation between the independent and dependent variable after accounting for the effect of the mediator. When CIs of the indirect effect of a mediator do not include 0, the effect is considered statistically significant (Preacher & Hayes, 2008). See Figure 1 for a graphic representation of the tested model. Finally, three additional mediation analyses were conducted using the symptom severity of each of the DSM-IV PTSD symptom clusters (reexperiencing, avoidance/numbing, and hyperarousal) as separate outcome variables. Results In our sample, TI scores ranged from 3 to 36 (M = 22.96, SD = 8.21), guilt scores ranged from 0 to 8 (M = 1.30, SD = 2.27),
Journal of Traumatic Stress DOI 10.1002/jts. Published on behalf of the International Society for Traumatic Stress Studies.
723
Tonic Immobility, Guilt, and PTSD
A Tonic immobility
Path C B = 1.25**, SE = 0.35
PTSD symptom severity
B Path A
Guilt
B = 0.07*, SE = 0.03
Tonic immobility
Path B B = 5.47**, SE = 1.35
Path C’ B = 0.89**, SE = 0.33
PTSD symptom severity
Figure 1. Graphic representation of the mediation model. (A) Tonic immobility affects posttraumatic stress disorder (PTSD) symptom severity. (B) Tonic immobility exerts effects on PTSD symptom severity through guilt. *p < .05. **p < .01.
and PTSD severity scores ranged from 0 to 125 (M = 37.52, SD = 28.32). Bivariate correlations indicated that all variables were significantly correlated (rs ranged from .25 to .52; all ps < .05). As hypothesized, the results of the regression-based model examining the role of guilt in the association between TI and PTSD symptom severity provided evidence consistent with mediation, F(2, 60) = 15.96, R2 = .34, B = 0.35, standard error = 0.14, bootstrapped 95% CI of indirect effects [0.10, 0.66] (see Fig. 1). The percentage of the total effect due to the indirect effect was 28%. Findings from the three additional models using the PTSD symptom clusters as the dependent variables were also consistent with mediation. Specifically, for the reexperiencing cluster, bootstrapped 95% CI of indirect effects was [0.02, 0.28]; for the avoidance/numbing cluster it was [0.04, 0.33]; and for the arousal cluster [0.02, 0.20]. All Fs exceeded 8.00, all R2 s > .21, all Bs > 0.07.
if clinicians can help their patients understand that the nature of TI dictates that they cannot fight back (vs. choosing not to fight back), it may help these patients reduce self-blaming cognitions and PTSD symptoms. This possibility awaits empirical testing. The current study is not without limitations. The use of a cross-sectional design prohibited the determination of causal relationships. The study was also limited by a modest sample size. A larger sample would provide further confidence in these results, and would allow for examination of whether these relationships vary as a function of other factors (e.g., trauma type). In addition, it would allow for determination of whether TI is associated with other forms of psychopathology (e.g., depression, alcohol abuse) and whether guilt also mediates these associations. Another limitation is that the study only included female participants and had a large number of exclusion criteria, both of which limit generalizability. In addition, we used a single item to measure posttraumatic guilt, which may not have fully captured this construct. The fact that this item (which served as our mediator) was part of the same interview as our outcome variable (PTSD symptoms) introduces the possibility that common method effects may have influenced the results. Future studies should examine this question using a more robust measure of guilt. Our model was also vulnerable to the problem of omitted variables because the mediator was not randomly assigned. Further, we were unable to examine whether time since the index event influenced results because PTSD symptoms were assessed in relation to all Criterion A events experienced, rather than in relation to one index event. Finally, like most studies examining peritraumatic variables, the possibility of response and memory biases may have impacted report of TI. Our findings suggest that guilt may be one mechanism by which trauma survivors who experience TI during their traumas later develop PTSD symptoms. It is possible that by educating these individuals about TI and thereby challenging inappropriate beliefs about self-blame, therapists will be able to decrease guilt and subsequently reduce PTSD symptom severity.
Discussion Our results suggest that the role of guilt in the association between TI and PTSD severity is consistent with mediation. TI among humans is a relatively newly studied area, and this is the first study to demonstrate guilt as a potential mechanism linking TI and PTSD symptoms. Our findings are consistent with literature suggesting that passivity during a trauma is associated with guilt (e.g., Lee et al., 2001), and with findings that guilt is associated with PTSD (e.g., Henning & Frueh, 1997). These results highlight the importance of educating individuals who have experienced TI and subsequently develop PTSD symptoms. Education about the involuntary nature of TI may reduce guilt about peritraumatic behavioral passivity, which may in turn reduce PTSD symptoms. Further, clinicians may be able to use this information to challenge their patients’ negative cognitions about their role during the trauma. For example,
References Abrams, M. P., Carleton, R., Taylor, S., & Asmundson, G. G. (2009). Human tonic immobility: Measurement and correlates. Depression and Anxiety, 26, 550–556. doi:10.1002/da.20462 American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: Author. Blake, D. D., Weathers, F. W., Nagy, L. M., Kaloupek, D. G., Gusman, F. D., Charney, D. S., & Keane, T. M. (1995). The development of a clinician-administered PTSD scale. Journal of Traumatic Stress, 8, 75–90. doi:10.1002/jts.2490080106 First, M., Spitzer, R., Williams, J., & Gibbon, M. (2000). Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I). In American Psychiatric Association (Ed.), Handbook of psychiatric measures (pp. 49–53). Washington, DC: American Psychiatric Association. Forsyth, J. P., Marx, B., Fus´e, T. M. K., Heidt, J., & Gallup, G. G., Jr. (2000). The Tonic Immobility Scale–Adult Form. Albany, NY: Author.
Journal of Traumatic Stress DOI 10.1002/jts. Published on behalf of the International Society for Traumatic Stress Studies.
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Bovin et al.
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Journal of Traumatic Stress DOI 10.1002/jts. Published on behalf of the International Society for Traumatic Stress Studies.
