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Psychological Medicine, Page 1 of 7. f 2007 Cambridge University Press doi:10.1017/S0033291707000682 Printed in the United Kingdom

Prognostic indices with brief and standard CBT for panic disorder : II. Moderators of outcome M I C H A E L G. T. D O W 1 *, J U S T I N A. K E N A R D Y 2 , D E R E K W. J O H N S T O N 3 , M I C H E L L E G. N E W M A N 4 , C. B A R R T A Y L O R 5 A N D A I L E E N T H O M S O N 6 1

NHS Fife, Department of Clinical Psychology, Stratheden Hospital, Cupar, Fife, UK; 2 Centre for National Research on Disability and Rehabilitation Medicine, and School of Psychology, University of Queensland, Brisbane, Queensland, Australia ; 3 Department of Psychology, Kings College, University of Aberdeen, UK; 4 Department of Psychology, Pennsylvania State University, PA, USA; 5 Department of Psychiatry and Behavioral Science, Stanford University School of Medicine, Stanford, CA, USA ; 6 Health Psychology Department, Gloucestershire Royal Hospital, Gloucester, UK

ABSTRACT Background. Despite the growth of reduced therapist-contact cognitive behavioural therapy (CBT) programmes, there have been few systematic attempts to determine prescriptive indicators for such programmes vis-a`-vis more standard forms of CBT delivery. The present study aimed to address this in relation to brief (6-week) and standard (12-week) therapist-directed CBT for panic disorder (PD) with and without agoraphobia. Higher baseline levels of severity and associated disability/comorbidity were hypothesized to moderate treatment eﬀects, in favour of the 12-week programme. Method. Analyses were based on outcome data from two out of three treatment groups (n=72) from a recent trial of three forms of CBT delivery for PD. The dependent variables were a continuous composite panic/anxiety score and a measure of clinical signiﬁcance. Treatmentrpredictor interactions were examined using multiple and logistic regression analyses. Results. As hypothesized, higher baseline severity, disability or co-morbidity as indexed by strength of dysfunctional agoraphobic cognitions ; duration of current episode of PD ; self-ratings of panic severity ; and the 36-item Short Form Health Survey (SF-36) (Mental component) score were all found to predict poorer outcome with brief CBT. A similar trend was apparent in relation to baseline level of depression. With high and low end-state functioning as the outcome measure, however, only the treatmentragoraphobic cognitions interaction was found to be signiﬁcant. Conclusions. While there was no evidence that the above variables necessarily contraindicate the use of brief CBT, they were nevertheless associated with greater overall levels of post-treatment improvement with the 12-week approach. where more apparent than in the management of anxiety disorders, and panic disorder (PD) in particular, for which there is increasing evidence for the eﬃcacy of reduced therapistcontact cognitive behavioural therapy (CBT) in a range of formats, including bibliotherapy (Gould et al. 1993 ; Febbraro et al. 1999), computer-delivered programmes (Newman et al. 1997; White et al. 2000 ; Carlbring et al. 2001 ; Kenardy et al. 2003 ; Lange et al. 2003 ; Kenwright & Marks, 2004) and brief, condensed versions of standard CBT delivery (Coˆte´ et al.

INTRODUCTION Increasing demand over the past three decades, among both ‘consumer ’ and ‘supplier’, for more cost-eﬀective and accessible treatments for common mental health disorders has reinforced a corresponding growth of brief, self-administered cognitive-behavioural interventions. This is no* Address for correspondence: Dr Michael G. T. Dow, Department of Psychology, University of Stirling, Stirling FK9 4LA, UK. (Email : [email protected])

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1994 ; Clark et al. 1999). Marks (2002) had identiﬁed these developments and the determination of their eﬀectiveness as partial evidence of CBT’s ‘coming of age’ as a therapeutic science. However, he also notes that we have made much less progress in our ability to predict outcome and identify those individuals for whom particular treatments may or may not be indicated. Following convention, the term ‘predictors ’ is used here to refer to baseline variables that show similar relationships with outcome irrespective of treatment assignment (Kraemer et al. 2002). However, moderators, sometimes referred to as ‘ prescriptive indicators ’ (Whisman, 1993), are baseline variables not inﬂuenced by treatment, but which inﬂuence outcome diﬀerentially and so relate to whom or under what circumstances a given treatment may be eﬀective. Thus, variables such as age, gender, severity and duration of disorder may function as moderators if they identify patient subgroups who respond diﬀerentially to diﬀerent treatments. While the identiﬁcation of predictors of CBT outcome is of obvious clinical value, as Hollon & Najavits (1988) observed, ‘only [moderators] are actually useful in the selection of treatment for a given patient’ (p. 651). An analysis of moderating eﬀects on outcome may be particularly relevant to brief, reduced therapist-contact CBT, as distinct from standard and other potentially more costly forms of CBT delivery, for several reasons. First, the identiﬁcation of prescriptive indicators and contraindicators for brief vis-a`-vis standard CBT would facilitate optimal treatment selection, further enhancing its eﬀectiveness and eﬃciency. Second, several researchers in this area have reported fairly high variability of response to minimal contact regimes across a range of disorders including sexual dysfunction (Mathews et al. 1976; Dow, 1983), eating disorders (Wilson et al. 2000) and generalized anxiety (Durham et al. 2004). Similarly, Kenardy et al. (2003), in their comparison of three forms of CBT delivery for PD involving a ‘standard ’ 12-session therapist-delivered CBT programme (CBT12) and two ‘ brief ’ six-session versions (one computer-assisted, CBT6CA, and the other therapist-directed only, CBT6), found all treatments to be eﬀective, but CBT12 to be signiﬁcantly superior to CBT6 on several key post-

treatment measures. CBT6CA occupied an intermediate position, being non-signiﬁcantly diﬀerent from the other two treatments. These diﬀerences were no longer apparent at the 6-month follow-up. Again, however, a higher degree of variability of response to CBT6 at post-treatment compared to the standard approach was apparent on most measures. In discussing such general ﬁndings, it has been proposed that this more variable response to brief forms of intervention may be due, in part at least, to the diﬀerence between standard and brief therapies in terms of the opportunity and time aﬀorded to therapists in identifying and resolving common obstacles to behavioural progress, including signiﬁcant co-morbidity; strongly held core dysfunctional beliefs ; and primary or secondary social, marital or other related problems (Mathews et al. 1976 ; Dow, 1983). On this basis such factors may thus be hypothesized to contribute to a diﬀerential responsiveness to the two forms of treatment delivery : that is these variables may have a moderating eﬀect on outcome (Dow, 1982). In the examination of eﬀect moderators from the trial of Kenardy et al. (2003), a comparison between CBT12 and CBT6 is probably of greatest theoretical interest, the two programmes being essentially identical in content and method of delivery, diﬀering only with respect to frequency of therapist contact. Moreover, this particular comparison is considered of broader relevance to general clinical practice, where there is more widespread uptake of brief CBT approaches but still very limited use of computers in treatment (Whitﬁeld & Williams, 2004). Hypothesis Because of statistical and other limitations, moderator (and mediator) analyses are often predominantly ‘exploratory and hypothesisgenerating rather than conclusive or hypothesistesting ’ (RUPP Anxiety Study Group, 2003, p. 14). In the present study, however, it may be hypothesized that patients with greater baseline levels of panic severity and associated disability (including degree of co-morbidity, agoraphobic avoidance and impairment of social and occupational functioning, as well as strength and frequency of dysfunctional agoraphobic cognitions) would respond less well to brief (sixsession) therapist-directed CBT compared to

Prognostic indices with CBT for PD : moderators of outcome

Table 1. Potential eﬀect moderators of brief (6-week) and standard (12-week) CBT for panic disorder with/without agoraphobia : variables on which analysis conducted Interviewer ratings of panic severity Frequency of panic attacks Duration of current episode of panic disorder Age of ﬁrst onset of panic symptoms Duration of anxiolytic use Duration of antidepressant use Self-ratings Patient ratings of panic severity Fear Questionnaire (Marks & Mathews, 1979) Subscales: Agoraphobia Social Phobia Blood/Injury Mobility Inventory for Agoraphobia (Chambless et al. 1985) Body Sensations Questionnaire (Chambless et al. 1984) Agoraphobic Cognitions Questionnaire (Chambless et al. 1984) State-Trait Anxiety Inventory (Spielberger et al. 1970) Beck Depression Inventory (Beck et al. 1988) Medical Outcomes Survey Short Form : SF-36 (Ware & Sherbourne, 1992) Factors : Mental and Physical Sheehan Disability Scale : Secondary Impairment of Work ; Social and Family Life (Sheehan, 1986)

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et al. (2002). For the main continuous dependent measure (i.e. the post-treatment composite panic/anxiety score), a series of simultaneous multiple regression analyses was conducted, each involving the three variables of interest (treatment, predictor and treatmentrpredictor interaction), while controlling for pretreatment composite panic/anxiety score, which was forced to enter the equation before the predictors of interest. Additional logistic regression analyses were conducted using clinically signiﬁcant posttreatment end-state as the dependent variable, essentially to determine whether any signiﬁcant interaction eﬀects from the above analysis would be replicated for this more stringent measure of outcome. Signiﬁcant interaction eﬀects from multiple regression were plotted using the procedure recommended by Cohen & Cohen (1983), and as described by Aiken & West (1991). RESULTS

‘standard ’ (12-session) therapist-directed CBT, in view of the greater opportunity in the latter condition to identify, assess and resolve such diﬃculties. METHOD All data for this and for the ﬁrst part of the present study were derived from the randomized controlled trial of CBT for PD reported in full elsewhere (Kenardy et al. 2003). Details of the sample, method of recruitment, the treatments and outcome measures have thus been documented previously in detail both in the original report and in the ﬁrst part of this study and are therefore not repeated here. Analysis In the present study the moderators analysis involves examining whether a baseline or prerandomization characteristic has an interactive eﬀect with treatment on outcome ; that is, do the eﬀects of treatment for individual subjects depend on the value of the variable in question ? The full list of potential moderators is shown in Table 1. Data on these variables were initially centred before forming the interaction term using the procedure recommended by Kraemer

The analysis of treatmentrpredictor interaction eﬀects focused exclusively on the comparison between standard (CBT12) and brief (CBT6) treatments for several reasons noted above. The results, shown in Tables 2 and 3, provide partial support for the hypothesis that patients presenting with more severe levels of PD, those with additional co-morbidity, and those with stronger dysfunctional cognitions relating to health and well-being would be more responsive to CBT12. Thus, signiﬁcant interaction eﬀects with treatment (CBT12 and CBT6) were found on four pretreatment measures relating to panic disorder severity. These signiﬁcant interaction eﬀects included frequency of dysfunctional agoraphobic cognitions, patients’ ratings of panic severity, duration of current panic episode and pre-treatment score on SF-36 (Mental). These moderator eﬀects were all in the predicted direction, each favouring CBT12 at higher pretreatment levels of severity. Fig. 1 illustrates the nature of this diﬀerential treatment response in relation to baseline strength of dysfunctional agoraphobic cognitions. Essentially the same relationship was replicated for each of the other signiﬁcant interaction eﬀects. While a signiﬁcant moderator eﬀect was found for pretreatment

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Table 2. Simultaneous multiple regression analyses : signiﬁcant moderating eﬀects of speciﬁc pretreatment variables on treatment outcome (Post-treatment Composite Panic/Anxiety Measure) B

S.E.

b

t

p

Regression 1 : Agoraphobic Cognitions Questionnaire (ACQ) Pretreatment Composite Treatment ACQ TreatmentrACQ R=0.680 ; adjusted R2=0.430 ; F(4, 67) 14.41, p=0.000 ; DR2a=0.141, p=0.001

0.587 x0.398 x0.016 0.466

0.142 0.126 0.113 0.167

0.512 x0.289 x0.017 0.254

4.137 x3.171 x0.139 2.788

0.000 0.002 0.890 0.007

Regression 2 : SF-36 (Mental) Pretreatment Composite Treatment SF-36 (Mental) TreatmentrSF-36 (Mental) R=0.677, adjusted R2=0.425, F(4, 65)=13.78, p=0.000 ; DR2a=0.137, p=0.002

0.683 x0.400 0.007 0.025

0.129 0.128 0.007 0.011

0.591 x0.287 0.117 0.207

5.310 x3.123 1.050 2.236

0.000 0.003 0.298 0.029

Regression 3 : Duration of Current Panic Episode Pretreatment Composite Treatment Duration of Current Panic Episode TreatmentrDuration of Current Panic Episode R=0.658, adjusted R2=0.398, F(4, 64)=12.24, p=0.000 ; DR2a=0.125, p=0.005

0.633 x0.382 0.008 x0.040

0.108 0.131 0.008 0.017

0.553 x0.275 0.093 x0.237

5.853 x2.918 0.933 x2.368

0.000 0.005 0.354 0.021

Regression 4 : Client Rating of Panic Severity Pretreatment Composite Treatment Client Panic Severity Rating TreatmentrClient Panic Severity Rating R=0.684, adjusted R2=0.436, F(4, 67)=14.74, p=0.000 ; DR2a=0.146, p=0.001

0.686 x0.384 x0.057 x0.191

0.126 0.123 0.044 0.072

0.599 x0.278 x0.142 x0.238

5.439 x3.115 x1.296 x2.655

0.000 0.003 0.200 0.010

Regression 5 : Beck Depression Inventory (BDI)b Treatment BDI TreatmentrBDI R=0.499, adjusted R2=0.215, F(3, 66)=7.29, p=0.000

x0.464 0.023 x0.030

0.149 0.007 0.014

x0.332 0.341 x0.230

x3.105 3.141 x2.120

0.003 0.003 0.038

Predictor

S.E., a b

Standard error. When compared with the model involving Pretreatment Composite Score only. In case of BDI, interaction eﬀect with treatment signiﬁcant only in absence of control for Pretreatment Composite Score.

Table 3.

Results of separate logistic regression analyses of treatmentrpredictor interaction eﬀects in relation to high/low end-state functioning 95% CI for exp b

Interaction with treatment Agoraphobic Cognitions Questionnaire SF-36 (Mental) Duration of Current Panic Episode Client Panic Severity Rating Beck Depression Inventory

b

S.E.

Wald

Signiﬁcance

exp b

Lower

Upper

x1.51 x0.07 0.09 0.33 0.05

0.68 0.04 0.07 0.28 0.05

4.98 2.86 1.66 1.44 0.92

0.03 0.09 0.20 0.23 0.34

0.22 0.93 1.09 1.39 1.05

0.06 0.85 0.96 0.81 0.95

0.83 1.01 1.24 2.38 1.15

level of depression, as measured by the BDI, this was apparent only when control for the pretreatment composite score was excluded. No signiﬁcant interaction eﬀects, however, were found for other measures of co-morbidity, baseline frequency of panic attacks or degree of agoraphobic avoidance. With high and low endstate functioning as the dependent variable, only

the treatmentragoraphobic cognitions interaction was found to be signiﬁcant (Table 3). DISCUSSION Despite the growth of brief self-help CBT interventions, there has been, in general, very

Prognostic indices with CBT for PD : moderators of outcome

Post-treatment composite anxiety

High Anxiety −0·25

−0·75

−1·25

−1·75

Low Anxiety −2·25 −1·6 −1·2 −0·8 −0·4 High Frequency

0

0·4

0·8 1·2 1·6 Low Frequency

Pre-treatment agoraphobic cognitions (ACQ) FIG. 1. Results of linear regression analysis showing interaction eﬀect between CBT format : CBT6 (%- - -%) and CBT12 (&—&) and baseline frequency of dysfunctional agoraphobic cognitions (Centred Equation) in relation to post-treatment composite anxiety score.

little research interest in the prescriptive indicators for their use, relative to more standard forms of CBT delivery. This may be in part because moderator analyses have a number of limitations and signiﬁcant interaction eﬀects are often diﬃcult to detect statistically (Shadish & Sweeney, 1991 ; McClelland & Judd, 1993). In the present study, based on outcome data from a prior comparison of a ‘ standard’ 12-week CBT programme and a comparable but condensed 6-week programme (Kenardy et al. 2003), several signiﬁcant treatmentrpredictor interaction eﬀects on post-treatment outcome, as measured by the composite panic/anxiety score, were found. These involved agoraphobic cognitions ; quality of life (SF-36 – Mental factor) ; patients’ ratings of panic severity ; and duration of current panic disorder episode, all in the predicted direction. Thus, while there was no difference between brief and standard treatments for those patients with less severe baseline scores on each of these measures, brief therapy in each case had a less positive eﬀect than standard 12-session CBT for those more severely disabled on the above speciﬁc measures. This is not to imply that brief therapy is contraindicated for those patients. An examination of pre–post therapy change for those patients in each of the two treatment groups, whose pretreatment scores were within the ‘most severe ’ quartile on

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each of the above measures, showed signiﬁcant pre–post therapy improvements of at least p< 0.05 (two-tailed). The degree of change, however, was signiﬁcantly greater in each case among those receiving CBT12. That those with more severe panic symptoms and dysfunctional automatic interpretations about bodily sensations, of the type considered central to a cognitive theory of panic, should be more responsive to a treatment format that affords greater opportunity to help challenge those beliefs, seems entirely reasonable. A similar argument applies also, of course, to the almost signiﬁcant relationship between pretreatment depression and the diﬀerential responsiveness to the two treatments in the reduction of panic and anxiety symptoms. A key function of therapist contact in CBT is identifying and resolving cognitive, emotional, motivational, social and other impediments to behavioural progress during largely self-administered homework tasks, before establishing new goals and assignments for the next interval between contacts (Mathews et al. 1976). It follows that those with more severe diﬃculties in areas central to the maintenance of the primary disorder, such as mood/motivation, and a consistent and wellestablished pattern of misattribution of bodily sensations, should require more therapist contact than those with fewer or less severe problems of this type and ideally more than that which brief therapy allows. That these factors appear to be related to a more general proﬁle of greater clinical severity, which would favour more frequent direct therapist contact, is reﬂected in the striking consistency of the moderator eﬀects, encompassing patients’ self-ratings of overall severity of panic, duration of the current episode and poorer perceived quality of mental well-being. These results have implications for future outcome studies in this area as strong moderators should be considered as stratiﬁcation variables. The identiﬁcation of predictors and moderators of outcome will of course be limited by the nature and range of variables on which data are collected in outcome trials. In addition to intra-personal factors, there are numerous other inter-personal and environmental variables of potential moderating inﬂuence in relation to brief and standard length CBT for PD. For example, the relationship between degree of

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adaptive partner support and compliance with exposure homework sessions for agoraphobia has been well documented (Mathews et al. 1981). That interpersonal factors of this kind may diﬀerentially inﬂuence the eﬀects of brief and standard length treatments, for reasons akin to the hypothesized moderating eﬀects above, seems reasonable but it was not possible to examine them here. Therefore, as Kraemer et al. (2002) point out, while moderator analysis is post hoc, ‘the decision to perform such an analysis must be a priori ’ (p. 882). Nevertheless, the burden of data collection is necessarily limited by both ethical and practical concerns and perhaps the most we may reasonably plan is the gradual accumulation of reliable prognostic and prescriptive indicators over time to guide the use of speciﬁc therapies. Research of this type also highlights the importance in clinical trials of detailed speciﬁcation of sample characteristics. Treatment effectiveness in clinical practice will depend on factors that extend beyond type of intervention and the nature of the disorder. Suﬃcient detail on motivational factors, co-morbidity, social adjustment, marital status and stability, for example, are rarely provided and this study is not beyond similar criticism. There is also a need for a standard set of measures being used across related eﬃcacy and eﬀectiveness trials to permit comparison and potential corroboration of results. We are still a long way from being able to answer the question posed by Paul forty years ago : ‘what treatment, by whom, is most eﬀective for this individual with that speciﬁc problem, and under which set of circumstances ?’ (Paul, 1967). Nevertheless, continued examination of the moderators and mediators of CBT outcome will no doubt begin to produce some answers. DECLARATION OF INTEREST None. REFERENCES Aiken, L. S. & West, S. G. (1991). Multiple Regression : Testing and Interpreting Interactions. Sage Publications : Newbury Park. Beck, A. T., Steer, R. A. & Garbin, M. G. (1988). Psychometric properties of the Beck Depression Inventory : twenty-ﬁve years of evaluation. Clinical Psychology Review 8, 77–100.

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