Psychological Reports: Disability & Trauma 2014, 114, 1, 1-13. © Psychological Reports 2014
VALIDITY OF THE ITALIAN VERSION OF THE SEVERITY OF DEPENDENCE SCALE (SDS) FOR NICOTINE DEPENDENCE IN SMOKERS INTENDING TO QUIT1, 2 MARIA CATERINA GRASSI
AMY K. FERKETICH
Department of Physiology and Pharmacology Sapienza University of Rome
Division of Epidemiology The Ohio State University College of Public Health
DOMENICO ENEA
FRANCO CULASSO
Centro Policlinico senza Fumo Policlinico Umberto I
Department of Public Health and Infectious Diseases PAOLO NENCINI
Department of Physiology and Pharmacology Sapienza University of Rome Summary.—The objective was to test the psychometric properties of an Italian version of the Severity of Dependence Scale, a five-item measure designed to assess the compulsive dimension of drug dependence. 635 smokers enrolled in a tobacco dependence treatment program served as the participants. The Fagerström Test for Nicotine Dependence was used as a comparative measure. Dimensionality of the Severity of Dependence Scale and the Fagerström Test for Nicotine Dependence was assessed by factor analysis. Prediction of smoking at one year was evaluated by logistic regression. Factor analysis yielded a two-factor solution; however, the second factor explained very little variance. Factor 1 had a Cronbach's α of .66 (overall Scale coefficient = .44). The total Severity of Dependence Score predicted smoking at one year (OR = 1.10).
Consistent with experimental evidence that nicotine is self-administered by laboratory animals (O'Dell & Khroyan, 2009), the addictive potential of tobacco smoking is demonstrated in humans as far as most smokers maintain the habit despite the fact that they want to quit and are aware that they are harming their health (Stolerman & Jarvis, 1995; Fiore, Address correspondence to Maria Caterina Grassi, M.D., Associate Professor of Pharmacology, Department of Physiology and Pharmacology “V. Erspamer,” Sapienza University of Rome 5, Piazzale Aldo Moro - 00161 Rome, Italy or e-mail ([email protected]). 2 The authors are grateful to Piero Mancini, M.S., for his help in creating the database and analysis of the data; to Stefania Pasquariello, M.S., for her help in collecting data; and to Rosanna Marchetti, sociologist, and Francesca Zanusso for their help in entering the data. This study has been supported by the Sapienza University of Rome. No conflict of interest is declared. MCG, AF, and PN designed the study, wrote the protocol, and participated in the writing of the manuscript. AF and FC conducted the statistical analyses, while DE ran the tobacco dependence treatment program and collected the data. All authors contributed to and have approved the final manuscript. 1
DOI 10.2466/18.15.PR0.114k16w7
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Jaén, Baker, Bailey, Benowitz, Curry, et al., 2008). Consequently, in 1980 the American Psychiatric Association (APA) proposed diagnostic criteria for nicotine dependence in the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM, American Psychiatric Association, 1980). These criteria were updated in subsequent editions and are based on the principle that the essential feature of tobacco dependence “is a cluster of cognitive, behavioral, and physiologic symptoms that indicate that the person has impaired control of psychoactive substance use and continues use of the substance despite adverse consequences” (American Psychiatric Association, 1987). This principle has been elaborated on in the framework of the Substance Dependence Syndrome, originally developed for alcohol dependence and then extended to a host of other psychoactive substances (Edwards & Gross, 1976). An important consequence of this principle is that all the substance abuse syndromes can be “diagnosed using a single set of ‘generic criteria.’” Although theoretically sound, the nosological criteria of DSM have shown several weaknesses when empirically tested. In particular, in the case of nicotine dependence DSM diagnostic criteria are inadequate to provide an accurate diagnosis and to predict smoking cessation (DiFranza & Sanouri Ursprung, 2010). Hence, the proposal is for a radical revision, given that DSM-IV criteria have not been used in tobacco research because of their ambiguous nature (Baker, Breslau, Covey, & Shiffman, 2012). Measures of nicotine dependence not based on the DSM have been developed, and the Fagerström Test for Nicotine Dependence (FTND) (Heatherton, Kozlowski, Frecker, & Fagerström, 1991) has emerged as the most widely used in practice and in research (Fiore, et al., 2008). It consists of six items that measure a single underlying factor, and its ability to predict abstinence and relapse has been repeatedly tested as it is closely related to biochemical indices of heavy smoking (Heatherton, et al., 1991). Empirical investigation demonstrated that the Fagerström Test for Nicotine Dependence is weakly correlated with DSM criteria for a series of measures of nicotine dependence (Hughes, Oliveto, Riggs, Kenny, Liguori, Pillitteri, et al., 2004). This has led some to conclude that the DSM may be more sensitive to diagnosing individuals who have mental health issues or additional dependencies (DiFranza & Sanouri Ursprung, 2010). It may also be that nicotine dependence does not fit the basic principle of Substance Dependence Syndrome, i.e., the common set of generic criteria that supposedly accounts for any kind of drug dependence. Relying on case series of tobacco smokers, DiFranza and Sanouri Ursprung (2010) have recently proposed that “recurrent compulsion to use tobacco is pathognomonic for nicotine dependence, and on this basis it has been proposed that the identification of this symptom is all, i.e., required to make a diagnosis.”
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The Severity of Dependence Scale (SDS) is a five-item questionnaire designed to measure the compulsive dimension of drug dependence (Gossop, Darke, Griffiths, Hando, Powis, Hall, et al. 1995; Gossop, Best, Marsden, & Strang, 1997). Besides showing high sensitivity, specificity, and predictive ability of persistent drug abuse, the Severity of Dependence Scale provided concurrent validity with DSM dependence criteria in the case of cocaine and heroin (González-Sáiz, Domingo-Salvany, Barrio, SánchezNiubó, Brugal, de la Fuente, et al., 2009), cannabis misuse among people with psychosis (Hides, Dawe, Young, & Kavanagh, 2007), or alcohol dependence (Lawrinson, Copeland, Gerber, & Gilmour, 2007). In spite of its ability to tap the compulsive dimension of substance dependence, as well as its concurrent validity with DMS criteria, to our knowledge, the Severity of Dependence Scale has never been used to evaluate the severity of nicotine dependence. In the present study, the Severity of Dependence Scale and the Fagerström Test for Nicotine Dependence were administered to a series of smokers enrolled in a tobacco dependence treatment program. Research Question. Would the Severity of Dependence Scale, designed to generalize among addictive drugs but also evaluating the compulsive dimension of dependence, have concurrent validity with the Fagerström Test for Nicotine Dependence—a measure specifically designed to assess nicotine dependence— in terms of predicting smoking cessation? METHOD Participants All individuals provided written informed consent to participate in the study. The study procedures were approved by the ethics review board of Policlinico Umberto I, at Sapienza University of Rome. The participants in this study were smokers who were enrolled in a tobacco dependence treatment program in Rome. The program has been described previously (Grassi, Enea, Marchetti, Caricati, & Nencini, 2006; Grassi, Enea, Ferketich, Lu, Pasquariello, & Nencini, 2011). Briefly, between January 2005 (when the Italian indoor smoking ban was introduced) and December 2010, 635 individuals (366 women: Mdn age = 49.6 yr., SD = 10.4, range 24–75; 269 men: Mdn age = 50.0 yr., SD = 11.0, range 18–78) who were motivated to quit smoking completed a 6-wk. group counseling program for smoking cessation at Policlinico Umberto I, Sapienza University of Rome. Participants had to be at least 18 yr. old and the registration fee was 100 Euros. Procedure The tobacco dependence treatment program (Grassi, et al., 2006; Grassi, et al., 2011) consisted of a baseline session lasting about 60 min., one
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week before the quit day. During this preliminary session, the program was explained, participants received a physical examination by the medical staff, underwent a structured interview about their smoking history, and exhaled carbon monoxide (CO) was measured (Smokerlyzer monitor, Bedfont Scientific Ltd., Rochester, England; cutoff: 10 ppm). Following this baseline were five consecutive days of counseling, and then one session per week for four consecutive weeks. All participants received cognitive behavioral treatment and during the preliminary session, in the absence of specifical medical problems, they had the option to concurrently receive, starting 10 days before the quit day, pharmacological therapy that consisted of: (a) nicotine replacement therapy, or (b) bupropion for a 7-wk. period, or (c) varenicline (starting in 2007) for a 12-wk. period, as per tobacco treatment guidelines (Fiore, et al., 2008). Follow-up assessments to verify continuous abstinence were carried out at 12, 26, and 52 wk. after the quit day. Follow-up of all participants ended in December 2011. Measures and Procedure The structured interview contained a variety of questions on tobacco use, demographics, and nicotine dependence. Participants were also asked to complete a Visual Analogue Scale to measure the intensity of their “craving to smoke” during the previous 7 days (Maxwell, 1978; Nicholson, 1978). On a self-efficacy test, the participants rated themselves from 1 to 10 (1: Not likely, 10: Very likely) on the possibility of “becoming a nonsmoker” (Bandura, 1977; Grassi, Enea, Ferketich, Lu, & Nencini, 2009). The Beck Depression Inventory (BDI) was administered to measure the severity of self-reported depression (Beck & Steer, 1978). Two scales were used to measure tobacco dependence: the Fagerström Test for Nicotine Dependence (FTND) and the Severity of Dependence Scale (SDS). The Fagerström Test for Nicotine Dependence has been translated into Italian and its properties have been presented previously (Ferketich, Fossati, & Apolone, 2008). The scale consists of six questions that ask about the time of the first cigarette during the day (Item 1), whether it is difficult for the person to not smoke when smoking is prohibited (Item 2), which cigarettes are most enjoyed during the day (Item 3), amount of cigarettes smoked daily (Item 4), whether the person smokes more upon waking or later in the day (Item 5), and whether the person smokes when he/she is ill (Item 6). These items are scored on a 3-point scale for Items 1 and 4 (Item 1, 0: 60 min., after wake up, 1: 31–60 min., after wake-up, 2: 6–30 min., after wake-up, 3: within 5 min., after wake-up; Item 4, 0: 10 or less, 1: 11–20, 2: 21–30, 3: 31 or more) and on a 2-point scale (for Items 2, 3, 5, 6, the scale was 0: No, 1: Yes) (Heatherton, et al., 1991). The Severity of Dependence Scale requires participants to think about their use of cigarettes during the past year. The questions and response options were translated into Italian by the authors (Grassi, Pisetzky, & Nen-
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cini, 2000; Grassi, Bencetti, Caricati, & Nencini, 2002) and then back translated into English. The Severity of Dependence Scale has five items: “Do you think your use of cigarettes is out of control?” (Item 1), “Does the prospect of missing a cigarette make you very anxious or worried?” (Item 2), “Do you worry about your use of cigarettes?” (Item 3), “Do you wish you could stop smoking?” (Item 4), and “How difficult would you find it to stop, or go without smoking?” (Item 5). These items are scored on a 3-point scale (for Items 1 to 4, 0: Never, 1: Sometimes; 2: Often; 3: Always; for Item 5, 0: Not difficult; 1: Quite difficult; 2: Very difficult; 3: Impossible) (Gossop, et al., 1995, 1997). Statistical Analysis Descriptive statistics were calculated for the entire sample. Exploratory factor analysis was performed using SAS Version 9.2 (Cary, NC) to assess whether the Severity of Dependence Scale for nicotine dependence was unidimensional, as it is for cocaine, amphetamine, and heroin dependence (Gossop, et al., 1995). Maximum likelihood was the method used for extraction, and an oblique rotation was performed (Costello & Osborne, 2005). A scree plot was examined to help decide the number of factors to retain. Items with loadings of .30 or higher were retained (Costello & Osborne, 2005). A similar analysis was performed for the Fagerström Test for Nicotine Dependence. To examine the internal consistency reliability of the Severity of Dependence Scale, Cronbach's α was calculated (Cronbach, 1951). Additionally, item-total correlations were calculated to assess the extent to which each item relates to the others in the scale. To assess convergent validity, the Severity of Dependence Scale and the Fagerström Test for Nicotine Dependence scores were correlated with baseline CO concentration using Spearman's nonparametric correlation. Finally, criterion validity was estimated by fitting a logistic regression model to estimate the association between the baseline Severity of Dependence Scale and Fagerström Test for Nicotine Dependence scores and smoking status at 12 mo. while controlling for the following variables: sex, age, years of schooling, baseline CO, BDI score, VAS rating of craving, and pharmacotherapy administered. Odds ratios (OR) and 95% confidence intervals (CI) were calculated. RESULTS Descriptive statistics for all demographics and measures are presented in Table 1. Over half of the participants were female and married, and slightly less than half lived with another smoker. The average age was 49.8 yr. (range 18–78) and the average number of years of education was 13.7, which is just over a high school education in Italy. The average number of years smoked was 32.5, and at baseline participants smoked a little over one pack of cigarettes per day and had an average CO of 23.2 ppm. The
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M. C. GRASSI, ET AL. TABLE 1 CHARACTERISTICS OF PARTICIPANTS FROM JANUARY 1, 2005, THROUGH DECEMBER 31, 2010 (N = 635), WITH DESCRIPTIVE STATISTICS ON ALL MEASURES Characteristic
M
SD
n
%
366
57.6
Single
150
23.6
Married
338
53.2
Divorced or separated or widowed
147
23.2
280
44.1
0
105
16.5
1
173
27.3
2
153
24.1
204
32.1
145
22.8
Females Age, yr.
49.8
10.7
Education, yr.
13.7
3.3
Marital status
Years of smoking
32.5
11.0
Exhaled carbon monoxide, ppm
23.2
12.5
Number of cigarettes per day
22.8
9.6
Other smokers in household (yes)
Number of quit attempts:
3+ Baseline Beck Depression Inventory (0–63) Number of cups of coffee per day
11.6
7.3
3.5
1.8
61.5
20.8
No alcohol consumption Craving Scale (0–100) Self-efficacy evaluation (0–10)
5.7
2.2
Severity of Dependence Scale
9.8
2.4
Range = 3–15, Mdn = 10
Fagerström Test for Nicotine Dependence
5.5
2.1
Range = 0–10, Mdn = 6
majority of participants had made at least one quit attempt in the past and 87.1% scored above 40 on the VAS scale for craving. The average BDI score was slightly above the cut-point of 10 for elevated symptoms of depression. Finally, participants consumed on average 3.5 cups of coffee per day and 476 (75%) drank two units of alcohol per day or less, 14 (2%) drank more than two units of alcohol per day, while 145 (23%) did not drink alcohol at all. Factor Structure of Scales Descriptive statistics for the Severity of Dependence Scale and the Fagerström Test for Nicotine Dependence scales, as well as the results from the factor analysis, are presented in Table 2. The factor analysis results for the Severity of Dependence Scale suggested a two-factor solu-
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SEVERITY OF DEPENDENCE FOR NICOTINE TABLE 2 ITEM-TOTAL CORRELATIONS AND FACTOR ANALYSIS OF SEVERITY OF DEPENDENCE SCALE AND FAGERSTRÖM TEST FOR NICOTINE DEPENDENCE Scale and Items
Item-total r Factor 1 Loading Factor 2 Loading
h2
Severity of Dependence Scale Item 1 (use out of control)
.15
–.03
.31
0.10
Item 2 (missing smoke causes worry)
.28
–.01
.76
0.58
Item 3 (worry about use)
.28
.99
.09
0.98
Item 4 (wish to stop)
.17
.50
–.06
0.26
Item 5 (how difficult to stop)
.29
.53
0.29
Variance explained Fagerström Test for Nicotine Dependence
.05 59.1%
3.0%
Factor 1
Factor 2
Item 1 (time of 1st cigarette in day)
.48
.65
.30
0.51
Item 2 (difficult not to smoke)
.19
.27
.02
0.07
Item 3 (cigarette hate most to give up)
.16
–.03
.51
0.27
Item 4 (number smoked per day)
.30
.65
–.04
0.43
Item 5 (smoke on waking)
.37
.20
.61
0.42
Item 6 (smoke when ill)
.37
.35
.28
0.21
Variance explained 2.0% 1.3% Note.— Item-total correlations were calculated within the Severity of Dependence Scale and Fagerström Test for Nicotine Dependence, respectively. Boldface indicates major loadings.
tion. The loadings of items from the two tests on each factor are presented in Table 2. Using a criterion of .30 for the loadings (Costello & Osborne, 2005), Factor 1 contained Items 3 and 4, and Factor 2 contained Items 1, 2, and 5 of the Severity of Dependence Scale. Because of the low amount of variance explained by Factor 2, the remaining results will only focus on Factor 1. The first factor contains questions related to motivation to quit (concern about smoking and willingness to quit). The results for the Fagerström Test for Nicotine Dependence scale are shown in Table 2. Factor 1 contained items 1, 4, and 6, whereas Factor 2 contained items 1, 3, and 5. The amount of variance explained by these factors is low, however. For Factor 1 of the Severity of Dependence Scale, the Cronbach α = .66, and for all five items, α = .44. For all items of the Fagerström Test for Nicotine Dependence, Cronbach α = .57. Spearman correlation coefficients were calculated between baseline CO levels and scores on the two tests for dependence. Factor 1 of the Se-
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verity of Dependence Scale was not statistically significantly correlated with baseline CO (r = .03). As expected, the Fagerström Test for Nicotine Dependence score was moderately and significantly correlated with baseline CO (r = .41, p < .001). Logistic Regression to Predict Smoking Status at 12 Months Using logistic regression analyses to predict continued smoking at 12 mo. (coded 0 = not smoking, 1 = smoking), the Fagerström Test for Nicotine Dependence scores and the Severity of Dependence Scale scores both predicted continued smoking. It is important to note that the primary independent variables, the two baseline scores, were modeled as continuous variables. Typically, when variables are modeled as continuous variables, the odds ratios are close to 1.0. The last part of the analysis addressed how well the first factor of the Severity of Dependence Scale predicted continued smoking after 12 mo. Factor 1 (Items 3 and 4) was not a significant predictor of continued smoking at 12 mo. Using a cut-point of 6 or higher (versus less than 6), the Fagerström Test for Nicotine Dependence score was significantly related to continue smoking after 12 mo. (see Table 3). TABLE 3 SPEARMAN CORRELATIONS AND A LOGISTIC REGRESSION PREDICTING 12-MO. SMOKING STATUS FROM SEVERITY OF DEPENDENCE SCALE AND FAGERSTRÖM TEST FOR NICOTINE DEPENDENCE Predictor
Spearman Correlation 2
3
4
Odds of Smoking at 1 Year OR
95%CI
Severity of Dependence Scale 1. Total score
.71
2. Factor 1 (Items 3, 4)
.44
.39
1.10†
1.02, 1.19
.35
.29
1.07
0.96, 1.19
.87
1.13†
1.04, 1.24
1.88‡
1.32, 2.68
Fagerström Test for Nicotine Dependence 3. Total score 4. Scores ≥ 6 vs scores < 6 †p < .01. ‡p < .001.
DISCUSSION The factor structure, internal consistency, and predictive ability of the Severity of Dependence Scale were evaluated when administered at baseline to smokers enrolling in a tobacco dependence treatment program. The Fagerström Test for Nicotine Dependence served as a comparative measure. The results presented in this paper differed from those reported by other researchers who examined the Severity of Dependence Scale for other psychotropic drugs (Gossop, et al., 1995; de las Cuevas, Sanz, de la
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Fuente, Padilla, & Berenguer, 2000; Hides, et al., 2007; González-Sáiz, et al., 2009) in that two dimensions of smoking behavior were found in the present study. However, only the first factor explained a significant proportion of the variance. The first factor contained Items 3 and 4, which appear to be motivational in the sense that the first evaluates the concern about being a smoker and the second the willingness to stop smoking. The second factor included the three items that address the emotional and behavioral components of compulsive smoking. While this construct is likely important for smoking cessation research, the fact that so little of the variance was explained by these three questions is troublesome. Future work could focus on creating better questions to capture these components. Cronbach's α coefficient approached the conventional threshold of .70 for Factor 1. Results obtained in this study are at odds with those obtained in studies where the five questions of the Severity of Dependence Scale have been found to converge on a single factor with a high Cronbach's α coefficient, with values between .81 and .90, when tested among individuals who were dependent on other psychoactive drugs, such as heroin, cocaine, and amphetamine (Gossop, et al., 1995). The unidimensionality of the Severity of Dependence Scale has been supported in heroin users (González-Sáiz, et al., 2009), khat chewers (Kassim, Islam, & Croucher, 2010), young cannabis smokers (Martin, Copeland, Gates, & Gilmour, 2006), and patients suffering of chronic headache and abuse of analgesics (Lundqvist, Aaseth, Grande, Benth, & Russell, 2010). However, a two-factor structure (Items 2, 4, and Items 1, 3, 5, respectively), was instead obtained for the version of the Severity of Dependence Scale assessing Ecstasy dependence, with factors similar to those identified in DSM-IV dependence criteria symptoms for ecstasy (Bruno, Matthews, Topp, Degenhardt, Gomez, & Dunn, 2009). Moreover, in their study of the Severity of Dependence Scale among a non-clinical sample of heroin users, González-Sáiz, Lozano, Ballesta, Silva, Brugal, Bilbao, et al. (2008) found that Items 3 and 4 differed from the other three in an item response theory analysis. Individuals were more consistent with the model expectations of item response theory when answering Items 3 and 4 than Items 1, 2, and 5, suggesting that all the items on the test do not measure the same construct. This situation is in some way reproduced in the present study. Considering that, as described above in the introduction section, nicotine dependence deviates from the diagnostic criteria of DMS, we may speculate that the two-factor structure found in this study reflects basic differences between nicotine and the other substance producing dependency. With respect to the Fagerström Test for Nicotine Dependence, the study confirms the already observed low internal consistency of the questionnaire, with a Cronbach's α value below the recommended 0.70 (Breteler, Hilberink,
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Zeeman, & Lammers, 2004; Courvoisier & Etter, 2010). Previous research findings on the factor structure of the Fagerström Test for Nicotine Dependence have been mixed. In their original analysis, Heatherton, et al. (1991) reported a single factor structure. Later studies have reported a two-factor structure of the Fagerström Test for Nicotine Dependence. Radzius, Gallo, Epstein, Gorelick, Cadet, and Uhl, et al. (2003) found that Factor 1 contained Items 1, 3, and 5 and Factor 2 contained Items 1, 2, 4, and 6. These results are similar to the current findings; however, the two factors explain different amounts of the variance (with magnitudes reversed from Radzius, et al.) and Item 2 had a loading just under .30. Breteler, et al. (2004) reported a two-factor structure, one factor comprising Items 2 and 4, with face validity for compulsivity. Previous examinations of the Fagerström Test for Nicotine Dependence have found that the factor(s) explain more of the variance than this study was able to in the current sample. Smokers in most previous studies, however, were not enrolled in a tobacco dependence treatment program and were thus not motivated to quit smoking. This could explain some of the discrepant results. Similar to the report that the Fagerström Test for Nicotine Dependence correlates with plasma cotinine, a metabolite of nicotine (Pomerleau, Pomerleau, Majchrzak, Kloska, & Malakuti, 1990), the test correlated moderately with expired breath CO. Moreover, similar to previous studies (Ferguson, Patten, Schreder, Offord, Eberman, & Hurt, 2003; Fidler, Shahab, & West, 2011), baseline Fagerström Test for Nicotine Dependence scores higher than 6 were predictive of still being a smoker one year later. There are some limitations that must be noted. Firstly, since the present study was conducted on individuals who were enrolled in a tobacco dependence treatment program, it is possible that they are not representative of the general population of smokers. Further research, possibly comparing the Severity of Dependence Scale with other compulsive scales of nicotine dependence in individuals who are not interested in quitting smoking, is required to resolve this issue. Secondly, some of the data are quite old; the enrollment in the program started in January 2005. Hence it is possible than some uncontrolled variable has been introduced during the long enrollment. Yet, it is important to note that the major change in the smoking behavior in Italy has been caused by the introduction of the indoor smoking ban that preceded the enrollment of smokers in this study. Considering the social and policy environments, enrollment was conducted in a rather stable setting. REFERENCES
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GOSSOP, M., DARKE, S., GRIFFITHS, P., HANDO, J., POWIS, B., HALL, W., & STRANG, J. (1995) The Severity of Dependence Scale (SDS): psychometric properties of the SDS in English and Australian samples of heroin, cocaine and amphetamine users. Addiction, 90, 607-614. GOSSOP, M., BEST, D., MARSDEN, J., & STRANG, J. (1997) Test-retest reliability of the Severity of Dependence Scale. Addiction, 92, 353-354. GRASSI, M. C., BENCETTI, M. L., CARICATI, A. M., & NENCINI, P. (2002) Predictive factors of persisting illicit drug use in hospitalized heroin addicts. Pharmacological Research, 46, 539-544. GRASSI, M. C., ENEA, D., FERKETICH, A. K., LU, B., & NENCINI, P. (2009) A smoking ban in public places increases the efficacy of bupropion and counseling on cessation outcomes at 1 yr. Nicotine & Tobacco Research, 11, 1114-1121. GRASSI, M. C., ENEA, D., FERKETICH, A. K., LU, B., PASQUARIELLO, S., & NENCINI, P. (2011) Effectiveness of varenicline for smoking cessation: a 1-yr. follow-up study. Journal of Substance Abuse Treatment, 41, 64-70. GRASSI, M. C., ENEA, D., MARCHETTI, R., CARICATI, A. M., & NENCINI, P. (2006) Combined counseling and bupropion therapy for smoking cessation: identification of outcome predictors. Drug Development Research, 67, 271-279. GRASSI, M. C., PISETZKY, F., & NENCINI, P. (2000) L’approccio tossicologico alla clinica delle tossicodipendenze: scelta ragionata delle scale di intensità della dipendenza [Toxicologic approach to the clinical aspects of drug dependence: rational choice of dependence evaluation scales]. Annali Istituto Superiore di Sanità, 36, 3-8. HEATHERTON, T. F., KOZLOWSKI, L. T., FRECKER, R. C., & FAGERSTRÖM, K. O. (1991) The Fagerström test for nicotine dependence: a revision of the Fagerström Tolerance Questionnaire. British Journal of Addiction, 86, 1119-1127. HIDES, L., DAWE, S., YOUNG, R. M., & KAVANAGH, D. J. (2007) The reliability and validity of the Severity of Dependence Scale for detecting cannabis dependence in psychosis. Addiction, 102, 35-40. HUGHES, J. R., OLIVETO, A. H., RIGGS, R., KENNY, M., LIGUORI, A., PILLITTERI, J. L., & MACLAUGHLIN, M. A. (2004) Concordance of different measures of nicotine dependence: two pilot studies. Addictive Behaviors, 29, 1527-1539. KASSIM, S., ISLAM, S., & CROUCHER, R. (2010) Validity and reliability of a Severity of Dependence Scale for khat (SDS–khat). Journal of Ethnopharmacology, 132, 570-577. LAWRINSON, P., COPELAND, J., GERBER, S., & GILMOUR, S. (2007) Determining a cut-off on the Severity of Dependence Scale (SDS) for alcohol dependence. Addictive Behaviors, 32, 1474-1479. LUNDQVIST, C., AASETH, K., GRANDE, R. B., BENTH, J. S., & RUSSELL, M. B. (2010) The severity of dependence score correlates with medication overuse in persons with secondary chronic headaches: the Akershus study of chronic headache. Pain, 148, 487-491. MARTIN, G., COPELAND, J., GATES, P., & GILMOUR, S. (2006) The Severity of Dependence Scale (SDS) in an adolescent population of cannabis users: reliability, validity and diagnostic cut-off. Drug and Alcohol Dependence, 83, 90-93. MAXWELL, C. (1978) Sensitivity and accuracy of the visual analogue scale: a psychophysical classroom experiment. British Journal of Clinical Pharmacology, 6, 15-24. NICHOLSON, A. N. (1978) Visual analogue scales and drug effects in man. British Journal of Clinical Pharmacology, 6, 3-4. O'DELL, L. E., & KHROYAN, T. V. (2009) Rodent models of nicotine reward: what do they tell us about tobacco abuse in humans? Pharmacology Biochemistry and Behavior, 91, 481-488.
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POMERLEAU, C. S., POMERLEAU, O. F., MAJCHRZAK, M. J., KLOSKA, D. D., & MALAKUTI, R. (1990) Relationship between nicotine tolerance questionnaire scores and plasma cotinine. Addictive Behaviors, 15, 73-80. RADZIUS, A., GALLO, J. J., EPSTEIN, D. H., GORELICK, D. A., CADET, J. L., UHL, G. E., & MOOLCHAN, E. T. (2003) A factor analysis of the Fagerström Test for Nicotine Dependence (FTND). Nicotine & Tobacco Research, 5, 255-260. STOLERMAN, P., & JARVIS, J. (1995) The scientific case that nicotine is addictive. Psychopharmacology, 117, 2-10. Accepted November 27, 2013.
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VALIDITY OF THE ITALIAN VERSION OF THE SEVERITY OF DEPENDENCE SCALE (SDS) FOR NICOTINE DEPENDENCE IN SMOKERS INTENDING TO QUIT1, 2 MARIA CATERINA GRASSI
AMY K. FERKETICH
Department of Physiology and Pharmacology Sapienza University of Rome
Division of Epidemiology The Ohio State University College of Public Health
DOMENICO ENEA
FRANCO CULASSO
Centro Policlinico senza Fumo Policlinico Umberto I
Department of Public Health and Infectious Diseases PAOLO NENCINI
Department of Physiology and Pharmacology Sapienza University of Rome Summary.—The objective was to test the psychometric properties of an Italian version of the Severity of Dependence Scale, a five-item measure designed to assess the compulsive dimension of drug dependence. 635 smokers enrolled in a tobacco dependence treatment program served as the participants. The Fagerström Test for Nicotine Dependence was used as a comparative measure. Dimensionality of the Severity of Dependence Scale and the Fagerström Test for Nicotine Dependence was assessed by factor analysis. Prediction of smoking at one year was evaluated by logistic regression. Factor analysis yielded a two-factor solution; however, the second factor explained very little variance. Factor 1 had a Cronbach's α of .66 (overall Scale coefficient = .44). The total Severity of Dependence Score predicted smoking at one year (OR = 1.10).
Consistent with experimental evidence that nicotine is self-administered by laboratory animals (O'Dell & Khroyan, 2009), the addictive potential of tobacco smoking is demonstrated in humans as far as most smokers maintain the habit despite the fact that they want to quit and are aware that they are harming their health (Stolerman & Jarvis, 1995; Fiore, Address correspondence to Maria Caterina Grassi, M.D., Associate Professor of Pharmacology, Department of Physiology and Pharmacology “V. Erspamer,” Sapienza University of Rome 5, Piazzale Aldo Moro - 00161 Rome, Italy or e-mail ([email protected]). 2 The authors are grateful to Piero Mancini, M.S., for his help in creating the database and analysis of the data; to Stefania Pasquariello, M.S., for her help in collecting data; and to Rosanna Marchetti, sociologist, and Francesca Zanusso for their help in entering the data. This study has been supported by the Sapienza University of Rome. No conflict of interest is declared. MCG, AF, and PN designed the study, wrote the protocol, and participated in the writing of the manuscript. AF and FC conducted the statistical analyses, while DE ran the tobacco dependence treatment program and collected the data. All authors contributed to and have approved the final manuscript. 1
DOI 10.2466/18.15.PR0.114k16w7
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Jaén, Baker, Bailey, Benowitz, Curry, et al., 2008). Consequently, in 1980 the American Psychiatric Association (APA) proposed diagnostic criteria for nicotine dependence in the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM, American Psychiatric Association, 1980). These criteria were updated in subsequent editions and are based on the principle that the essential feature of tobacco dependence “is a cluster of cognitive, behavioral, and physiologic symptoms that indicate that the person has impaired control of psychoactive substance use and continues use of the substance despite adverse consequences” (American Psychiatric Association, 1987). This principle has been elaborated on in the framework of the Substance Dependence Syndrome, originally developed for alcohol dependence and then extended to a host of other psychoactive substances (Edwards & Gross, 1976). An important consequence of this principle is that all the substance abuse syndromes can be “diagnosed using a single set of ‘generic criteria.’” Although theoretically sound, the nosological criteria of DSM have shown several weaknesses when empirically tested. In particular, in the case of nicotine dependence DSM diagnostic criteria are inadequate to provide an accurate diagnosis and to predict smoking cessation (DiFranza & Sanouri Ursprung, 2010). Hence, the proposal is for a radical revision, given that DSM-IV criteria have not been used in tobacco research because of their ambiguous nature (Baker, Breslau, Covey, & Shiffman, 2012). Measures of nicotine dependence not based on the DSM have been developed, and the Fagerström Test for Nicotine Dependence (FTND) (Heatherton, Kozlowski, Frecker, & Fagerström, 1991) has emerged as the most widely used in practice and in research (Fiore, et al., 2008). It consists of six items that measure a single underlying factor, and its ability to predict abstinence and relapse has been repeatedly tested as it is closely related to biochemical indices of heavy smoking (Heatherton, et al., 1991). Empirical investigation demonstrated that the Fagerström Test for Nicotine Dependence is weakly correlated with DSM criteria for a series of measures of nicotine dependence (Hughes, Oliveto, Riggs, Kenny, Liguori, Pillitteri, et al., 2004). This has led some to conclude that the DSM may be more sensitive to diagnosing individuals who have mental health issues or additional dependencies (DiFranza & Sanouri Ursprung, 2010). It may also be that nicotine dependence does not fit the basic principle of Substance Dependence Syndrome, i.e., the common set of generic criteria that supposedly accounts for any kind of drug dependence. Relying on case series of tobacco smokers, DiFranza and Sanouri Ursprung (2010) have recently proposed that “recurrent compulsion to use tobacco is pathognomonic for nicotine dependence, and on this basis it has been proposed that the identification of this symptom is all, i.e., required to make a diagnosis.”
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The Severity of Dependence Scale (SDS) is a five-item questionnaire designed to measure the compulsive dimension of drug dependence (Gossop, Darke, Griffiths, Hando, Powis, Hall, et al. 1995; Gossop, Best, Marsden, & Strang, 1997). Besides showing high sensitivity, specificity, and predictive ability of persistent drug abuse, the Severity of Dependence Scale provided concurrent validity with DSM dependence criteria in the case of cocaine and heroin (González-Sáiz, Domingo-Salvany, Barrio, SánchezNiubó, Brugal, de la Fuente, et al., 2009), cannabis misuse among people with psychosis (Hides, Dawe, Young, & Kavanagh, 2007), or alcohol dependence (Lawrinson, Copeland, Gerber, & Gilmour, 2007). In spite of its ability to tap the compulsive dimension of substance dependence, as well as its concurrent validity with DMS criteria, to our knowledge, the Severity of Dependence Scale has never been used to evaluate the severity of nicotine dependence. In the present study, the Severity of Dependence Scale and the Fagerström Test for Nicotine Dependence were administered to a series of smokers enrolled in a tobacco dependence treatment program. Research Question. Would the Severity of Dependence Scale, designed to generalize among addictive drugs but also evaluating the compulsive dimension of dependence, have concurrent validity with the Fagerström Test for Nicotine Dependence—a measure specifically designed to assess nicotine dependence— in terms of predicting smoking cessation? METHOD Participants All individuals provided written informed consent to participate in the study. The study procedures were approved by the ethics review board of Policlinico Umberto I, at Sapienza University of Rome. The participants in this study were smokers who were enrolled in a tobacco dependence treatment program in Rome. The program has been described previously (Grassi, Enea, Marchetti, Caricati, & Nencini, 2006; Grassi, Enea, Ferketich, Lu, Pasquariello, & Nencini, 2011). Briefly, between January 2005 (when the Italian indoor smoking ban was introduced) and December 2010, 635 individuals (366 women: Mdn age = 49.6 yr., SD = 10.4, range 24–75; 269 men: Mdn age = 50.0 yr., SD = 11.0, range 18–78) who were motivated to quit smoking completed a 6-wk. group counseling program for smoking cessation at Policlinico Umberto I, Sapienza University of Rome. Participants had to be at least 18 yr. old and the registration fee was 100 Euros. Procedure The tobacco dependence treatment program (Grassi, et al., 2006; Grassi, et al., 2011) consisted of a baseline session lasting about 60 min., one
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week before the quit day. During this preliminary session, the program was explained, participants received a physical examination by the medical staff, underwent a structured interview about their smoking history, and exhaled carbon monoxide (CO) was measured (Smokerlyzer monitor, Bedfont Scientific Ltd., Rochester, England; cutoff: 10 ppm). Following this baseline were five consecutive days of counseling, and then one session per week for four consecutive weeks. All participants received cognitive behavioral treatment and during the preliminary session, in the absence of specifical medical problems, they had the option to concurrently receive, starting 10 days before the quit day, pharmacological therapy that consisted of: (a) nicotine replacement therapy, or (b) bupropion for a 7-wk. period, or (c) varenicline (starting in 2007) for a 12-wk. period, as per tobacco treatment guidelines (Fiore, et al., 2008). Follow-up assessments to verify continuous abstinence were carried out at 12, 26, and 52 wk. after the quit day. Follow-up of all participants ended in December 2011. Measures and Procedure The structured interview contained a variety of questions on tobacco use, demographics, and nicotine dependence. Participants were also asked to complete a Visual Analogue Scale to measure the intensity of their “craving to smoke” during the previous 7 days (Maxwell, 1978; Nicholson, 1978). On a self-efficacy test, the participants rated themselves from 1 to 10 (1: Not likely, 10: Very likely) on the possibility of “becoming a nonsmoker” (Bandura, 1977; Grassi, Enea, Ferketich, Lu, & Nencini, 2009). The Beck Depression Inventory (BDI) was administered to measure the severity of self-reported depression (Beck & Steer, 1978). Two scales were used to measure tobacco dependence: the Fagerström Test for Nicotine Dependence (FTND) and the Severity of Dependence Scale (SDS). The Fagerström Test for Nicotine Dependence has been translated into Italian and its properties have been presented previously (Ferketich, Fossati, & Apolone, 2008). The scale consists of six questions that ask about the time of the first cigarette during the day (Item 1), whether it is difficult for the person to not smoke when smoking is prohibited (Item 2), which cigarettes are most enjoyed during the day (Item 3), amount of cigarettes smoked daily (Item 4), whether the person smokes more upon waking or later in the day (Item 5), and whether the person smokes when he/she is ill (Item 6). These items are scored on a 3-point scale for Items 1 and 4 (Item 1, 0: 60 min., after wake up, 1: 31–60 min., after wake-up, 2: 6–30 min., after wake-up, 3: within 5 min., after wake-up; Item 4, 0: 10 or less, 1: 11–20, 2: 21–30, 3: 31 or more) and on a 2-point scale (for Items 2, 3, 5, 6, the scale was 0: No, 1: Yes) (Heatherton, et al., 1991). The Severity of Dependence Scale requires participants to think about their use of cigarettes during the past year. The questions and response options were translated into Italian by the authors (Grassi, Pisetzky, & Nen-
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cini, 2000; Grassi, Bencetti, Caricati, & Nencini, 2002) and then back translated into English. The Severity of Dependence Scale has five items: “Do you think your use of cigarettes is out of control?” (Item 1), “Does the prospect of missing a cigarette make you very anxious or worried?” (Item 2), “Do you worry about your use of cigarettes?” (Item 3), “Do you wish you could stop smoking?” (Item 4), and “How difficult would you find it to stop, or go without smoking?” (Item 5). These items are scored on a 3-point scale (for Items 1 to 4, 0: Never, 1: Sometimes; 2: Often; 3: Always; for Item 5, 0: Not difficult; 1: Quite difficult; 2: Very difficult; 3: Impossible) (Gossop, et al., 1995, 1997). Statistical Analysis Descriptive statistics were calculated for the entire sample. Exploratory factor analysis was performed using SAS Version 9.2 (Cary, NC) to assess whether the Severity of Dependence Scale for nicotine dependence was unidimensional, as it is for cocaine, amphetamine, and heroin dependence (Gossop, et al., 1995). Maximum likelihood was the method used for extraction, and an oblique rotation was performed (Costello & Osborne, 2005). A scree plot was examined to help decide the number of factors to retain. Items with loadings of .30 or higher were retained (Costello & Osborne, 2005). A similar analysis was performed for the Fagerström Test for Nicotine Dependence. To examine the internal consistency reliability of the Severity of Dependence Scale, Cronbach's α was calculated (Cronbach, 1951). Additionally, item-total correlations were calculated to assess the extent to which each item relates to the others in the scale. To assess convergent validity, the Severity of Dependence Scale and the Fagerström Test for Nicotine Dependence scores were correlated with baseline CO concentration using Spearman's nonparametric correlation. Finally, criterion validity was estimated by fitting a logistic regression model to estimate the association between the baseline Severity of Dependence Scale and Fagerström Test for Nicotine Dependence scores and smoking status at 12 mo. while controlling for the following variables: sex, age, years of schooling, baseline CO, BDI score, VAS rating of craving, and pharmacotherapy administered. Odds ratios (OR) and 95% confidence intervals (CI) were calculated. RESULTS Descriptive statistics for all demographics and measures are presented in Table 1. Over half of the participants were female and married, and slightly less than half lived with another smoker. The average age was 49.8 yr. (range 18–78) and the average number of years of education was 13.7, which is just over a high school education in Italy. The average number of years smoked was 32.5, and at baseline participants smoked a little over one pack of cigarettes per day and had an average CO of 23.2 ppm. The
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M. C. GRASSI, ET AL. TABLE 1 CHARACTERISTICS OF PARTICIPANTS FROM JANUARY 1, 2005, THROUGH DECEMBER 31, 2010 (N = 635), WITH DESCRIPTIVE STATISTICS ON ALL MEASURES Characteristic
M
SD
n
%
366
57.6
Single
150
23.6
Married
338
53.2
Divorced or separated or widowed
147
23.2
280
44.1
0
105
16.5
1
173
27.3
2
153
24.1
204
32.1
145
22.8
Females Age, yr.
49.8
10.7
Education, yr.
13.7
3.3
Marital status
Years of smoking
32.5
11.0
Exhaled carbon monoxide, ppm
23.2
12.5
Number of cigarettes per day
22.8
9.6
Other smokers in household (yes)
Number of quit attempts:
3+ Baseline Beck Depression Inventory (0–63) Number of cups of coffee per day
11.6
7.3
3.5
1.8
61.5
20.8
No alcohol consumption Craving Scale (0–100) Self-efficacy evaluation (0–10)
5.7
2.2
Severity of Dependence Scale
9.8
2.4
Range = 3–15, Mdn = 10
Fagerström Test for Nicotine Dependence
5.5
2.1
Range = 0–10, Mdn = 6
majority of participants had made at least one quit attempt in the past and 87.1% scored above 40 on the VAS scale for craving. The average BDI score was slightly above the cut-point of 10 for elevated symptoms of depression. Finally, participants consumed on average 3.5 cups of coffee per day and 476 (75%) drank two units of alcohol per day or less, 14 (2%) drank more than two units of alcohol per day, while 145 (23%) did not drink alcohol at all. Factor Structure of Scales Descriptive statistics for the Severity of Dependence Scale and the Fagerström Test for Nicotine Dependence scales, as well as the results from the factor analysis, are presented in Table 2. The factor analysis results for the Severity of Dependence Scale suggested a two-factor solu-
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SEVERITY OF DEPENDENCE FOR NICOTINE TABLE 2 ITEM-TOTAL CORRELATIONS AND FACTOR ANALYSIS OF SEVERITY OF DEPENDENCE SCALE AND FAGERSTRÖM TEST FOR NICOTINE DEPENDENCE Scale and Items
Item-total r Factor 1 Loading Factor 2 Loading
h2
Severity of Dependence Scale Item 1 (use out of control)
.15
–.03
.31
0.10
Item 2 (missing smoke causes worry)
.28
–.01
.76
0.58
Item 3 (worry about use)
.28
.99
.09
0.98
Item 4 (wish to stop)
.17
.50
–.06
0.26
Item 5 (how difficult to stop)
.29
.53
0.29
Variance explained Fagerström Test for Nicotine Dependence
.05 59.1%
3.0%
Factor 1
Factor 2
Item 1 (time of 1st cigarette in day)
.48
.65
.30
0.51
Item 2 (difficult not to smoke)
.19
.27
.02
0.07
Item 3 (cigarette hate most to give up)
.16
–.03
.51
0.27
Item 4 (number smoked per day)
.30
.65
–.04
0.43
Item 5 (smoke on waking)
.37
.20
.61
0.42
Item 6 (smoke when ill)
.37
.35
.28
0.21
Variance explained 2.0% 1.3% Note.— Item-total correlations were calculated within the Severity of Dependence Scale and Fagerström Test for Nicotine Dependence, respectively. Boldface indicates major loadings.
tion. The loadings of items from the two tests on each factor are presented in Table 2. Using a criterion of .30 for the loadings (Costello & Osborne, 2005), Factor 1 contained Items 3 and 4, and Factor 2 contained Items 1, 2, and 5 of the Severity of Dependence Scale. Because of the low amount of variance explained by Factor 2, the remaining results will only focus on Factor 1. The first factor contains questions related to motivation to quit (concern about smoking and willingness to quit). The results for the Fagerström Test for Nicotine Dependence scale are shown in Table 2. Factor 1 contained items 1, 4, and 6, whereas Factor 2 contained items 1, 3, and 5. The amount of variance explained by these factors is low, however. For Factor 1 of the Severity of Dependence Scale, the Cronbach α = .66, and for all five items, α = .44. For all items of the Fagerström Test for Nicotine Dependence, Cronbach α = .57. Spearman correlation coefficients were calculated between baseline CO levels and scores on the two tests for dependence. Factor 1 of the Se-
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M. C. GRASSI, ET AL.
verity of Dependence Scale was not statistically significantly correlated with baseline CO (r = .03). As expected, the Fagerström Test for Nicotine Dependence score was moderately and significantly correlated with baseline CO (r = .41, p < .001). Logistic Regression to Predict Smoking Status at 12 Months Using logistic regression analyses to predict continued smoking at 12 mo. (coded 0 = not smoking, 1 = smoking), the Fagerström Test for Nicotine Dependence scores and the Severity of Dependence Scale scores both predicted continued smoking. It is important to note that the primary independent variables, the two baseline scores, were modeled as continuous variables. Typically, when variables are modeled as continuous variables, the odds ratios are close to 1.0. The last part of the analysis addressed how well the first factor of the Severity of Dependence Scale predicted continued smoking after 12 mo. Factor 1 (Items 3 and 4) was not a significant predictor of continued smoking at 12 mo. Using a cut-point of 6 or higher (versus less than 6), the Fagerström Test for Nicotine Dependence score was significantly related to continue smoking after 12 mo. (see Table 3). TABLE 3 SPEARMAN CORRELATIONS AND A LOGISTIC REGRESSION PREDICTING 12-MO. SMOKING STATUS FROM SEVERITY OF DEPENDENCE SCALE AND FAGERSTRÖM TEST FOR NICOTINE DEPENDENCE Predictor
Spearman Correlation 2
3
4
Odds of Smoking at 1 Year OR
95%CI
Severity of Dependence Scale 1. Total score
.71
2. Factor 1 (Items 3, 4)
.44
.39
1.10†
1.02, 1.19
.35
.29
1.07
0.96, 1.19
.87
1.13†
1.04, 1.24
1.88‡
1.32, 2.68
Fagerström Test for Nicotine Dependence 3. Total score 4. Scores ≥ 6 vs scores < 6 †p < .01. ‡p < .001.
DISCUSSION The factor structure, internal consistency, and predictive ability of the Severity of Dependence Scale were evaluated when administered at baseline to smokers enrolling in a tobacco dependence treatment program. The Fagerström Test for Nicotine Dependence served as a comparative measure. The results presented in this paper differed from those reported by other researchers who examined the Severity of Dependence Scale for other psychotropic drugs (Gossop, et al., 1995; de las Cuevas, Sanz, de la
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Fuente, Padilla, & Berenguer, 2000; Hides, et al., 2007; González-Sáiz, et al., 2009) in that two dimensions of smoking behavior were found in the present study. However, only the first factor explained a significant proportion of the variance. The first factor contained Items 3 and 4, which appear to be motivational in the sense that the first evaluates the concern about being a smoker and the second the willingness to stop smoking. The second factor included the three items that address the emotional and behavioral components of compulsive smoking. While this construct is likely important for smoking cessation research, the fact that so little of the variance was explained by these three questions is troublesome. Future work could focus on creating better questions to capture these components. Cronbach's α coefficient approached the conventional threshold of .70 for Factor 1. Results obtained in this study are at odds with those obtained in studies where the five questions of the Severity of Dependence Scale have been found to converge on a single factor with a high Cronbach's α coefficient, with values between .81 and .90, when tested among individuals who were dependent on other psychoactive drugs, such as heroin, cocaine, and amphetamine (Gossop, et al., 1995). The unidimensionality of the Severity of Dependence Scale has been supported in heroin users (González-Sáiz, et al., 2009), khat chewers (Kassim, Islam, & Croucher, 2010), young cannabis smokers (Martin, Copeland, Gates, & Gilmour, 2006), and patients suffering of chronic headache and abuse of analgesics (Lundqvist, Aaseth, Grande, Benth, & Russell, 2010). However, a two-factor structure (Items 2, 4, and Items 1, 3, 5, respectively), was instead obtained for the version of the Severity of Dependence Scale assessing Ecstasy dependence, with factors similar to those identified in DSM-IV dependence criteria symptoms for ecstasy (Bruno, Matthews, Topp, Degenhardt, Gomez, & Dunn, 2009). Moreover, in their study of the Severity of Dependence Scale among a non-clinical sample of heroin users, González-Sáiz, Lozano, Ballesta, Silva, Brugal, Bilbao, et al. (2008) found that Items 3 and 4 differed from the other three in an item response theory analysis. Individuals were more consistent with the model expectations of item response theory when answering Items 3 and 4 than Items 1, 2, and 5, suggesting that all the items on the test do not measure the same construct. This situation is in some way reproduced in the present study. Considering that, as described above in the introduction section, nicotine dependence deviates from the diagnostic criteria of DMS, we may speculate that the two-factor structure found in this study reflects basic differences between nicotine and the other substance producing dependency. With respect to the Fagerström Test for Nicotine Dependence, the study confirms the already observed low internal consistency of the questionnaire, with a Cronbach's α value below the recommended 0.70 (Breteler, Hilberink,
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Zeeman, & Lammers, 2004; Courvoisier & Etter, 2010). Previous research findings on the factor structure of the Fagerström Test for Nicotine Dependence have been mixed. In their original analysis, Heatherton, et al. (1991) reported a single factor structure. Later studies have reported a two-factor structure of the Fagerström Test for Nicotine Dependence. Radzius, Gallo, Epstein, Gorelick, Cadet, and Uhl, et al. (2003) found that Factor 1 contained Items 1, 3, and 5 and Factor 2 contained Items 1, 2, 4, and 6. These results are similar to the current findings; however, the two factors explain different amounts of the variance (with magnitudes reversed from Radzius, et al.) and Item 2 had a loading just under .30. Breteler, et al. (2004) reported a two-factor structure, one factor comprising Items 2 and 4, with face validity for compulsivity. Previous examinations of the Fagerström Test for Nicotine Dependence have found that the factor(s) explain more of the variance than this study was able to in the current sample. Smokers in most previous studies, however, were not enrolled in a tobacco dependence treatment program and were thus not motivated to quit smoking. This could explain some of the discrepant results. Similar to the report that the Fagerström Test for Nicotine Dependence correlates with plasma cotinine, a metabolite of nicotine (Pomerleau, Pomerleau, Majchrzak, Kloska, & Malakuti, 1990), the test correlated moderately with expired breath CO. Moreover, similar to previous studies (Ferguson, Patten, Schreder, Offord, Eberman, & Hurt, 2003; Fidler, Shahab, & West, 2011), baseline Fagerström Test for Nicotine Dependence scores higher than 6 were predictive of still being a smoker one year later. There are some limitations that must be noted. Firstly, since the present study was conducted on individuals who were enrolled in a tobacco dependence treatment program, it is possible that they are not representative of the general population of smokers. Further research, possibly comparing the Severity of Dependence Scale with other compulsive scales of nicotine dependence in individuals who are not interested in quitting smoking, is required to resolve this issue. Secondly, some of the data are quite old; the enrollment in the program started in January 2005. Hence it is possible than some uncontrolled variable has been introduced during the long enrollment. Yet, it is important to note that the major change in the smoking behavior in Italy has been caused by the introduction of the indoor smoking ban that preceded the enrollment of smokers in this study. Considering the social and policy environments, enrollment was conducted in a rather stable setting. REFERENCES
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