Change Processes in Residential Cognitive Therapy for Bulimia Nervosa

Transcription

1 RESEARCH ARTICLE Change Processes in Residential Cognitive Therapy for Bulimia Nervosa Asle Hoffart 1,2 *,y, Hanne Lysebo 3, Bente Sommerfeldt 4 & Øyvind Rø 1 1 Research Institute, Modum Bad, Vikersund, Norway 2 Department of Psychology, University of Oslo, Norway 3 Crisis Resolution Team, Jessheim Region, Aker University Hospital, Oslo, Norway 4 Special Unit of Eating Disorders, Aker University Hospital, Oslo, Norway Abstract The purpose of the study was to examine the relationships of process variables derived from the cognitive model of bulimia nervosa (BN) and weekly outcome. The participants were 39 patients with BN or subthreshold bulimia consecutively admitted to an inpatient treatment program for bulimia. Theory-derived process and outcome variables were measured repeatedly during the course of therapy with a gap of a week between each measurement. The data were analysed with time series methods (ARIMA). Weekly variations in the process variables: self-efficacy about resisting binge eating, dysfunctional beliefs, negative affect and positive affect influenced variations in subsequent outcome, whereas weekly outcome did not influence subsequent process. These results are consistent with the cognitive model of BN and suggest that self-efficacy, dysfunctional beliefs, negative affect and positive affect are potential targets for treatment that need further investigation. Copyright # 2010 John Wiley & Sons, Ltd and Eating Disorders Association. Keywords bulimia nervosa; cognitive therapy; process outcome; time series *Correspondence Asle Hoffart, PhD, Research Institute, Modum Bad, N-3370 Vikersund, Norway. Tel: Fax: asle.hoffart@modum-bad.no y Professor. Published online in Wiley InterScience ( DOI: /erv.980 Introduction Bulimia nervosa (BN) is characterized by recurrent episodes of binge eating and maladaptive compensatory behaviour like self-induced vomiting, misuse of laxatives, strict dieting or vigorous exercise to prevent weight gain. A number of controlled treatment trials for BN has been published, indicating that cognitive behaviour therapy (CBT) is the most effective treatment (Fairburn & Harrison, 2003). An analysis of change processes in a therapy that works may serve both to evaluate the correctness of the model and to improve the therapy. The purpose of this study was to examine change processes in a residential treatment program for BN combining CBT and group dynamic therapy. Group dynamic therapy was included because group therapy appears to be a viable treatment modality for eating disorders (Wilfley et al., 2002) and because of a need to monitor and influence the group processes occurring anyway in a residential setting. CBT for BN is based on a cognitive model for what maintains the disorder (Fairburn, Cooper & Shafran, 2003). From this model, several mechanisms of change follow. One is a reduction in dietary restraint (Wilson,

2 Change Processes in Cognitive Therapy for Bulimia A. Hoffart et al. Fairburn, Agras, Walsh, & Kraemer, 2002). The more the patients adopt a regular pattern of flexible eating with normal amount of food, the less likely they are to binge eat and then purge. Wilson et al. (2002) found that reduction in dietary restraint at week 4 of treatment mediated posttreatment improvement in both binge eating and vomiting. Another is change in self-efficacy for coping with situations that trigger binge eating and purging (e.g. negative affect and interpersonal distress) (Wilson et al., 2002). Wilson and Fairburn (1993) found that self-efficacy was enhanced in CBT and that enhanced self-efficacy was associated with decrease in binge eating and purging. Wilson et al. (2002) found that self-efficacy concerning eating behaviour, negative affect and body shape and weight at midtreatment (Week 10) was associated with posttreatment outcome. Also other studies have evidenced a relationship between increased self-efficacy and improvement (Schneider, O Leary, & Agras, 1987; Wilson, Vitousek, & Loeb, 2000). Third, also a reduction in binge eating triggers themselves such as less frequency and/or intensity of negative affect should lead to less binge eating. A study of students in their natural environment indicated that negative affect influenced the course of bulimic symptoms (Stice, 2001). A fourth mechanism is the modification of dysfunctional attitudes about body shape and weight such as the belief that having a low weight and slender shape is a strong condition of selfworth (Wilson et al., 2002). Reducing shape and weight concerns should directly decrease the pressure to diet that is the proximal cause of binge eating. Existing therapy studies have either looked at concurrent relationships between change in process and outcome or at the effect of change in process on outcome after a single temporal lag of several months. However, studies of the course of bulimic symptoms indicate that they start to change early in therapy (Wilson et al., 2002) and this suggests that a much tighter temporal relationship exists between process factors and outcome. For example, changes in beliefs may have rapid effects on bulimic symptoms which could be observed after days, rather than months. Some studies of individuals with BN in their natural environment have examined the relationships between stress, mood and bulimic behaviour on a daily or momentary time level. Using daily measurements, Freeman and Gil (2004) found that higher levels of stress were associated with binge eating. Smyth et al. (2007) found that within a day, decreasing positive affect, increasing stress and increasing negative affect preceded bulimic behaviours. Both these findings confirm some of the assumptions of the cognitive model and extend them by suggesting the importance of positive affect. In the present study, process and outcome variables were measured repeatedly during the course of therapy with a gap of only a week between each measurement. The purpose was to examine all the four mechanisms of CBT described above. However, because our measure of weekly process and outcome was not able to differentiate between a dietary restraint/restriction factor and a binge eating/vomiting factor (see Subjects and methods section), we were not able to investigate the effect of reduced dietary restraint on binge eating and purging. Thus, more specifically, we explored the following research questions: (1) Does increased self-efficacy a week predict less bulimic symptoms the next week and/or the week thereafter? (2) Does increased self-efficacy a week predict less concern about body shape and weight the next week and/or the week thereafter? (3) Does decreased certainty of dysfunctional beliefs predict less bulimic symptoms the next week and/ or the week thereafter? (4) Does decreased certainty of dysfunctional beliefs predict less concern about body shape and weight the next week and/or the week thereafter? (5) Does less negative affect a week predict less bulimic symptoms the next week and/or the week thereafter? (6) Does less negative affect a week predict less concern about body shape and weight the next week and/or the week thereafter? (7) Does more positive affect a week predict less bulimic symptoms the next week and/or the week thereafter? (8) Does more positive affect a week predict less concern about body shape and weight the next week and/or the week thereafter? (9) Does less concern about body shape and weight a week predict less bulimic symptoms the next week and/or the week thereafter? Subjects and methods Participants and procedure The participants were 39 patients consecutively admitted to a treatment program for BN at Modum

3 A. Hoffart et al. Change Processes in Cognitive Therapy for Bulimia Bad, Vikersund, Norway. Modum Bad is a clinic established for the residential treatment of nonpsychotic patients that lack adequate local treatment opportunities or have not responded adequately to outpatient care and require more extensive and/or specialized treatment. The admission criteria were symptoms of BN that impaired daily functioning, inadequate responses to previous treatment and age older than 18. Those who met these criteria were fully informed about the study and gave written consent. The study was conducted in compliance with the regional ethics committee. The patients constituted six blocks of seven patients. Three of the 42 patients refused to participate in the study. The mean age of the 39 remaining patients, all female, was 29.0 years (SD ¼ 7.4, range ¼ 19 50). All were Caucasian. Mean age at onset of the eating disorder was 16.0 years (SD ¼ 4.7). Twenty-nine (36%) had been working at least half time during the last 6 months before admission, 45 (56%) were receiving sick or disability pay because of their mental illness, six (8%) were either unemployed, dependent on the income of their spouses or were studying. All the 39 patients had previously received psychiatric treatment. At admission, 27 (69%) met criteria for BN and 12 (31%) for eating disorder not otherwise specified (EDNOS). In all cases, EDNOS was subthreshold bulimia. Three of the patients dropped out of treatment at 5 7 weeks into the program. Treatment and treatment context The treatment was a multi-component 15 weeks program for BN and patients were admitted in closed groups of seven (Rø, Martinsen, Hoffart, & Rosenvinge, 2005). The focus of treatment was on normalizing eating patterns and reducing binge eating and compensatory behaviour. The treatment model was an integrated combination of CBT and group dynamic therapy, but no manual was used. The program consisted of four compulsory meals daily (containing 2000 kcal/day), weekly individual therapy sessions, CBT or group dynamic group sessions, physical activity, psychoeducation and art therapy sessions. There was almost no use of tranquillizers. The use of antidepressants was individually evaluated and medication was often tapered off due to limited effect. In the middle of the program, the patients were given one week leave at home to test out their new skills in their natural environment. Therapists The individual therapists were two clinical psychologists (2 and 3 years of psychiatric training), a medical doctor in psychiatric training having had 2 years of such training and a clinical social worker with 10 years of psychiatric training. The program included three experienced psychiatric nurses/occupational therapists, who conducted the group sessions together with the individual therapists. The therapists and the nurses/ occupational therapists conducting the CBT and dynamic group sessions were supervised by professionals who watched the sessions from behind a oneway mirror and who were knowledgeable about CBT and group dynamic therapy. In addition, the individual therapists were individually supervised on a weekly basis by experts from the therapists profession. Global measures and procedure The Eating Disorder Examination, version 12.0 (EDE 12.0) is a semi-structured interview, widely used in assessing eating disorder (ED) psychopathology and in generating DSM-IV-based ED diagnoses (Fairburn & Cooper, 1993). It consists of subscales for restraint, shape concern, weight concern and eating concern. The interview was performed by the individual patient s individual therapist. The therapists were trained to take the interview by conducting it the first two times together with the fourth author. Inter-rater reliability was not tested. The self-report Eating Disorder Inventory, second version (EDI-2) (Garner, Olmsted, & Polivy, 1991) consists of 11 subscales: drive for thinness, bulimia, body dissatisfaction, ineffectiveness, perfectionism, interpersonal distrust, interoceptive awareness, maturity fears, asceticism, impulse regulation and social insecurity. Weekly measures General outcome was measured by the 34-item Clinical Outcomes in Routine Evaluation Outcome Measure (CORE-OM) (Evans et al., 2002). The items cover four domains: subjective well-being (four items), problems/ symptoms (12 items), life functioning (12 items) and risk (to self and to others, six items). The CORE-OM has shown good internal and test retest reliability, good convergent validity with other instruments, large

4 Change Processes in Cognitive Therapy for Bulimia A. Hoffart et al. differences between clinical and non-clinical samples and good sensitivity to change. The items of the problems/symptoms domain describe anxiety, depression and somatic complaints and they were used in this study as a measure of negative affect. The subjective well-being scale was used as a measure of positive affect. Only these two subscales of the CORE-OM were analysed in the present study. Process and bulimic symptoms were measured by the Process Outcome Measure for Bulimia (POMB), which was constructed for this study. Table 1 lists the scales, their items and the names of the standard scales from which some of the items were taken. Two items cover restrictive eating behaviour, one item cover binge eating episodes and one item covers self-induced vomiting. Two additional items purported to measure the strength of dietary restraint and of urge to overeat, How many times have you resisted the urge to eat less the last week? and How many days have you resisted the urge to overeat the last week?, were omitted from further analysis (and the table) because they were found not to correlate with any of the other intermediate outcome items. Because the scores on the outcome items had highly skewed distributions, they were transformed to approach normality. The first item on number of the 28 meals eaten was transformed as follows: 26 or less ¼ 1, 27 ¼ 2 and 28 ¼ 3. The second item on number of days complied with foodlist was transformed as follows: 6 days or less ¼ 1, 7 days ¼ 2. The third item on vomiting was logarithmically transformed, and the fourth item on binge eating was transformed as follows: 0 1 episodes ¼ 1, 2 4 episodes ¼ 2, 4 6 episodes ¼ 3 and 7 episodes or more ¼ 4. The first two items were reversed. To examine the structure of these four bulimic behaviour symptoms, the transformed items were factors analysed with varimax rotation. This analysis yielded one factor with eigenvalue above 1, and the four items were, therefore, averaged to one scale for bulimic symptoms. One item measured exercising to control shape or weight. Three items measured self-efficacy about resisting binge eating (a) in response to interpersonal situations, (b) when experiencing negative affect and (c) in response to shape and weight cues, respectively. These items were selected from Wilson et al. s (2002) measure of self-efficacy about resisting binge eating. Three items measure dysfunctional beliefs, two of these concern unrealistic expectations for body weight and shape and one concerns the meaning of body shape/ weight in terms of self-worth (Spangler, 1999). One item represents a condensed version of Wilson et al. s (2002) two items of concern about weight and about shape to a measure of concern about shape and weight. To ensure that these eight items represent unique Table 1 Process scales: Internal consistencies (Cronbach s a) and items Bulimic symptoms y (a ¼.58) How many of the 28 regular meals the last week have you eaten? How many days the last week have you complied to your food list? How many times have you made yourself sick and vomited the last week? How many times have you had binge eating episodes the last week? (Binge eating means that you eat a clearly larger amount of food than is usually eaten under the circumstances and you experienced a loss of control over-eating at the time) Compensatory physical exercise How many times have you exercised the last week to control your weight or to burn off calories? Self-efficacy y (a ¼.94) How certain (0 100%) are you that you could successfully resist binge eating: if you had an argument with some one or felt rejected by someone? if you were anxious or depressed? if you were feeling fat or were to look at yourself in a full length mirror? Dysfunctional beliefs y (a ¼.87) How much do you believe (0 100%) in the thoughts: if I eat normally, I will gain weight if I gain a pound, I will keep gaining endlessly if I gain weight, I will be a failure and disgusting Concerns about shape and weight How dissatisfied have you felt about your body the last week? y Computed as mean scores across items

5 A. Hoffart et al. Change Processes in Cognitive Therapy for Bulimia factors, they were factor analysed (Kayser Meyer Olkin ¼.82), asking for four factors and using varimax rotation. The items loaded as expected. Based on these results, subscales were constructed for compensatory physical exercise (item 5) (not used in this study), selfefficacy (items 6 8), dysfunctional beliefs (items 9 11) and concern about body shape and weight (item 12). With the exception of the lower internal consistency of the bulimic symptoms measure, all measures were satisfactorily internally consistent (see Table 1). To examine the validity of the weekly outcome scales, the correlations between the overall outcome scales (EDE, EDI-2) scores at pretreatment and posttreatment and scores on the weekly outcome scales (bulimic symptoms, concern about body shape and weight) at corresponding points of time were computed. Bulimic symptoms correlated only with the maturity fears subscale of the EDI-2 (r ¼.39, p <.01). Concern about body shape and weight correlated with EDE weight concern (r ¼.38, p <.01), EDE shape concern (r ¼.43, p <.01) and EDI-2 body dissatisfaction (r ¼.43, p <.01). Assessment Assessment on the overall outcome measures took place in the first week after admission (pretreatment) and at discharge (posttreatment). The weekly measures were completed every Wednesday within half an hour after lunch and before a physical exercise session. The patients started completion about one week after admission but did not complete the measures during their one-week leave at home. The patients used from 5 to 20 minutes to complete the measures. To control for potential expectancy bias, the patients were informed that the therapists were blind to the patients weekly ratings. Statistics As we wanted to examine the temporal relationships between our repeated observations of process and our repeated observations of intermediate outcome, we used an analysis of concomitance in time series (Box, Jenkins, & Reinsel, 1994). That is, we investigated whether the process series of weekly data points (selfefficacy, dysfunctional beliefs, negative affect and positive affect) predicted the weekly outcome series (bulimic symptoms, concern about body shape and weight). The relationship between two series is the cross-correlation function. For example, the positive Lag 1 cross-correlation function for self-efficacy and bulimic symptoms is derived by pairing the self-efficacy score at week 1 with the symptoms score at Week 2. This procedure continues until the self-efficacy score the next last week is paired with the last week symptoms score. The positive Lag 2 cross-correlation is correspondingly derived by pairing self-efficacy scores with symptoms scores with a lag of 2 weeks. The crosscorrelation function is computed also for all possible negative lags, where symptoms precede self-efficacy. Thus, there are several possible relationships among the variables that can be investigated by time series analysis: whether a process variable predicts an outcome variable or vice versa, and at what lags. It is possible that the effects of process on outcome (or vice versa) may not be apparent immediately (within a week) perhaps not appearing until more than a week has passed. Because the length of the series for each patient is too short to be analysed separately, each of the outcome and process variables from the individual cases were arranged end to end to form long time series across patients, with two blank observations between each case. This led to a juncture between one individual s series and the next that is similar to seasonal effects in other types of time series. Furthermore, arranging two blanks between individuals prevented that crosscorrelations between series (see below) would involve relating different individuals at the two first lags. This procedure of connecting the individual series assumes that all these show the same structural characteristics (see below). Non-completed measures were not recorded as missing in the data files. Thus, in a few cases, the Lag 1 distance could be 2 weeks or more. Not only can process (e.g. self-efficacy) be correlated with outcome (e.g. symptoms) over time but also process and outcome can be correlated with itself over time. In fact, such longitudinal data from individuals are usually autocorrelated. This results from stable intrapersonal factors (gender, personality, etc.) and lead to adjacent observations within the same individual being more alike than two random observations from different individuals (Box et al., 1994). The presence of autocorrelations can cause misleading results in a time series analysis. Specifically, if both variables in an analysis are autocorrelated, a large cross-correlation coefficient (CCF) will result even when the two

6 Change Processes in Cognitive Therapy for Bulimia A. Hoffart et al. variables are not related. Therefore, the time series is first examined for the presence of autocorrelation and correlated error, and then transformed to reduce autocorrelation. In our study, we used an ARIMA procedure. To determine the specific ARIMA model to be used, each series was examined for pattern of autocorrelation and partial autocorrelation. An ARIMA (1,0,0) model a model with a first order autoregressive component produced uncorrelated residuals in most cases. One exception appeared: the series for dysfunctional beliefs was better filtered by an ARIMA (2,0,0) model. We then examined the CCF of the residuals from each of the series. Only the first two positive and negative lags of the cross-correlations were examined. Again, the reason for examining the second lags was to ensure that there were no process outcome relationships that appeared more slowly (more than a week delay). Although the present study is of a hypothesisgenerating nature (Kraemer, Wilson, Fairburn, & Agras, 2002) the large number of statistical tests and the power of the study led us to use the more conservative significance level of.01, two-tailed, to limit the number of Type I errors. We used the SPSS 13.0 program in the ARIMA analyses. Results Changes in binge eating and vomiting Twenty-two of 26 with a diagnosis of BN with purging had vomited the month before admission, the one with BN without purging had not vomited, four of the 11 with EDNOS with purging had vomited and the one with EDNOS without purging had not vomited. Most of the changes in binge eating and vomiting may occur in patients moving from their natural environment to the more socially controlled hospital milieu. To examine this possibility, we compared the number of weekly binge eating and vomiting episodes the month before admission (measured by the EDE) and number of binge eating and vomiting episodes the first and the last week of the hospital stay (measured by the relevant items of the POMB, see Table 1). Number of binge eating episodes did not change from before admission to the first week of treatment (Wilcoxon signed rank test: z ¼ 1.01, ns), but decreased from the first to the last week of treatment (Wilcoxon signed rank test: z ¼ 2.55, p <.05). Number of vomiting episodes, on the other hand, decreased from before treatment to the first week of treatment (Wilcoxon signed rank test: z ¼ 2.75, p <.01), but did not change from the first to the last week of treatment (Wilcoxon signed rank test: z ¼ 1.84, ns). The last result may express a floor effect as only 15 (39%) of the 39 patients reported to vomit the first week of treatment. Process results Summing across the 39 patients, the weekly measures were delivered to the patients 324 times. They were completed 298 times (92%). Among these 298 questionnaires with 3576 items to complete, there were 60 (1.7%) missing items. The cross-correlations between the ARIMA (1,0,0) or (2,0,0) produced residuals of the process variables and the weekly outcome variable are reported in Table 2. Five of our nine research questions were positively answered by the results. Increased self-efficacy a week predicted less bulimic symptoms the subsequent week. Increased selfefficacy a week also predicted less concern about body shape and weight the subsequent week. Decreased certainty of dysfunctional beliefs a week predicted less bulimic symptoms not the subsequent week but 2 weeks later. Decreased negative affect (CORE-OM problems/ symptoms) predicted less concern about body shape and weight the subsequent week. Increased positive affect (CORE-OM: subjective well-being) a week predicted less concern about bodily shape and weight the subsequent week. In none of the cases did the outcome variables bulimic symptoms and concern about body shape and weight predict the process variables, and there were no sequential relationships between the two outcome variables. To explore possible period effects, we repeated the cross-correlation analyses separately for the early (the first five assessments) and the late (the assessments after the fifth) period. The cross-correlations were similar across periods, except that the Lag 1 correlation between self-efficacy and concern about body shape and weight was only.03 early but.29 late. Discussion In contrast to previous studies of process in CBT for BN, the present study involved repeated assessment of

7 A. Hoffart et al. Change Processes in Cognitive Therapy for Bulimia Table 2 Cross-correlations between residuals of ARIMA weekly process and outcome variables at different lags First variable second variable Lag þ2 þ1 1 2 Self-efficacy Bulimic s Self-efficacy concern BSW Dys. beliefs Bulimic s Dys. beliefs concern BSW Negative affect Bulimic s Negative affect concern BSW Positive affect Bulimic s Positive affect concern BSW Concern BSW Bulimic s Note. þ2 ¼ process leads outcome with two lags (2 weeks); þ1 ¼ process leads outcome with one lag (1 week); 1 ¼ process lags outcome with one lag (1 week); 2 ¼ process lags outcome with two lags (2 weeks); Bulimic s. ¼ Bulimic symptoms; Dys. beliefs ¼ Dysfunctional beliefs; BSW ¼ Body Shape and Weight; SE¼.058 for all cross-correlations. p <.01 (two-tailed); p ¼.12; p ¼.17. both process and suboutcome and a time series approach was used. This approach effectively addresses the issues of early response in CBT and of assuring the time precedence of the process variable (Kraemer et al., 2002). Five of the nine research questions were positively answered by the results. First, increase in self-efficacy about resisting binge eating in response to stress a week predicted both less bulimic symptoms and less concern about body shape and weight the subsequent week. This finding on a weekly basis supports and extends previous findings on a more global time level (Schneider et al., 1987; Wilson & Fairburn, 1993; Wilson et al., 2000; Wilson et al., 2002). Furthermore, in contrast to our study, these previous studies have measured process and outcome in partly overlapping time periods and the sequential relationships of the variables could therefore not be established. Second, decreased certainty of dysfunctional beliefs a week predicted less bulimic symptoms not the subsequent week but 2 weeks later. Thus, this effect appeared more slowly than the other effects in this study. In the cognitive model of BN, it is assumed that dysfunctional beliefs affect dieting, which, in turn, affects over-eating. This sequence could not be fully investigated in our study because dieting and overeating did not separate as distinct factors among the items measuring bulimic behaviours. Third, decreased negative affect predicted less concern about body shape and weight the subsequent week. This finding supports both what Stice (2001) found on a more global time level in a community sample and what Smyth et al. (2007) found on a daily level in a naturalistic environment setting. Interestingly, also increased positive affect predicted less concern about body shape and weight the subsequent week, further supporting the findings of Smyth et al. (2007). The possibility that symptom change would precede cognitive therapy process, which has been suggested in studies of the relationship between cognitions and symptoms in cognitive therapy of depression (Kraemer et al., 2002) and in cognitive and interpersonal therapy of social phobia (Hoffart, Borge, Sexton, & Clark, 2009), did not receive empirical support here. Furthermore, there appeared to be few period (early vs. late) effects. A main limitation of this study was the low internal consistency of our weekly bulimic symptom measure. This may be related to the difficulty of assessing bulimic symptoms in an inpatient setting where eating and purging behaviour are much more controlled by the environment. More environmental control leads to lower level of and less variation in symptoms and therefore lower correlation between the items measuring these symptoms. In support of this assumption, the results indicated that number of vomiting episodes (although not number of over-eating episodes) decreased from before to just after admission to the hospital, but not during the hospital stay. The shift in bulimic behaviour from the natural to the hospital milieu may also explain the poor correlations between our weekly bulimic symptom measure and the

8 Change Processes in Cognitive Therapy for Bulimia A. Hoffart et al. overall outcome measures. The pretreatment level on the overall measures was based on the time before admission. Our second outcome measure, concern about body shape and weight, is not behavioural and should, therefore, be less context-dependent. In line with this assumption, it correlated moderately with relevant subscales of the overall outcome measures. Another limitation was that the treatment program included several components in addition to CBT (e.g. group dynamic therapy, hospitalization and some medication), and one cannot draw inferences from our results about the differential effects of the various components. The process effects described here are based on passive observation without manipulation of the process variables. Thus, it is possible that unmeasured events and experiences could explain the results. One should note that the sequential relationships between process and suboutcomes were obtained on a weekly time scale. Different relationships may prevail on a daily or moment-to-moment time scale. The measurement error of the repeated measures and the potential heterogeneity of the characteristics of the individual time series may attune the cross-correlations obtained and lead to Type II errors in the statistical conclusions. The lack of inter-rater reliability ratings of the eating disorder interview (EDE 12.0) conducted is also a limitation of the present study. A further limitation is the use of the patients individual therapists to conduct these interviews, which may lead both to biased reports from the patients and/or biased interviewer ratings. The study was theory-based, yet exploratory in nature. Although we used the more conservative significance level of.01, the possibility of Type I error remains high due to the large number of tests performed. The treatment was delivered in a residential context, and this has both advantages and disadvantages. First, the residential setting gives a unique possibility to standardize environmental influences when studying process and mediators of change. Second, and most important for our purposes, it provides the practical possibilities to collect process and short-term outcome data frequently and reliably. The disadvantages include uncertainties about generalizability to the more common outpatient setting and the difficulties of obtaining ecologically valid symptom ratings described above. Our study should be replicated in an outpatient setting. In conclusion, the results are consistent with the cognitive model of BN and suggest that self-efficacy, dysfunctional beliefs, negative affect and positive affect are potential targets for treatment that need further investigation. REFERENCES Box, G. E. P., Jenkins, G. M., & Reinsel, G. C. (1994). Time series analysis: Forecasting and control. Englewood Cliffs, NJ: Prentice Hall Inc. Evans, C., Connell, J., Barkham, M., Margison, F., McGrath, G., Mellor-Clark, J., et al. (2002). Towards a standardised brief outcome measure: Psychometric properties and utility of the CORE-OM. British Journal of Psychiatry, 180, Fairburn, C. G., & Cooper, Z. (1993). The eating disorder examination (12th ed.). In C. G. Fairburn, & G. T. Wilson, (Eds.), Binge eating: Nature, assessment and treatment. (pp ). London: Guilford. Fairburn, C. G., & Harrison, P. J. (2003). Eating disorders. Lancet, 361, Fairburn, C. G., Cooper, Z., & Shafran, R. (2003). Cognitive behaviour therapy for eating disorders: A transdiagnostic theory and treatment. Behaviour Research and Therapy, 41, Freeman, L. M., & Gil, K. M. (2004). Daily stress, coping, and dietary restraint in binge eating. International Journal of Eating Disorders, 36, Garner, D., Olmsted, M. P., & Polivy, J. (1991). Manual of eating disorders inventory-2 (EDI-2). Odessa: Psychological Assessment Resources. Hoffart, A., Borge, F. M., Sexton, H., & Clark, D. M. (2009). Change processes in residential cognitive and interpersonal psychotherapy for social phobia: A process-outcome study. Behavior Therapy, 40, Kraemer, H. C., Wilson, G. T., Fairburn, C. G., & Agras, W. S. (2002). Mediators and moderators of treatment effects in randomized clinical trials. Archives of General Psychiatry, 59, Rø, Ø., Martinsen, E. W., Hoffart, A., & Rosenvinge, J. (2005). Two-year prospective study of personality disorders in adults with longstanding eating disorders. International Journal of Eating Disorders, 37, Schneider, J. A., O Leary, A., & Agras, W. S. (1987). The role of perceived self-efficacy in recovery from bulimia: a preliminary examination. Behaviour Research and Therapy, 25, Smyth, J. M., Wonderlich, S. A., Heron, K. E., Sliwinski, M. J., Crosby, R. D., Mitchell, J. E., et al. (2007). Daily and

9 A. Hoffart et al. Change Processes in Cognitive Therapy for Bulimia momentary mood and stress are associated with binge eating and vomiting in bulimia nervosa patients in the natural environment. Journal of Consulting and Clinical Psychology, 75, Spangler, D. L. (1999). Cognitive-behavioral therapy for bulimia nervosa: An illustration. Journal of Clinical Psychology, 55, Stice, E. (2001). A prospective test of the dual-pathway model of bulimic pathology: Mediating effects of dieting and negative affect. Journal of Abnormal Psychology, 110, Wilfley, D. E., Welch, R. R., Stein, R. I., Spurrell, E. B., Cohen, L. R., Saelens, B. E., et al. (2002). A randomized comparison of group cognitive-behavioral therapy and group interpersonal psychotherapy for the treatment of overweight individuals with binge-eating disorder. Archives of General Psychiatry, 59, Wilson, G. T., Fairburn, C. C., Agras, W. S., Walsh, B. T., & Kraemer, H. (2002). Cognitive-behavioural therapy for bulimia nervosa: time course and mechanisms of change. Journal of Consulting and Clinical Psychology, 70, Wilson, G. T., & Fairburn, C. G. (1993). Cognitive treatments for eating disorders. Journal of Consulting and Clinical Psychology, 61, Wilson, G. T., Vitousek, K. M., & Loeb, K. L. (2000). Stepped care treatment for eating disorders. Journal of Consulting and Clinical Psychology, 68,