The mediational role of panic self-efficacy in cognitive behavioraltherapy for panic disorder: A systematic review and meta-analysis
Hanne N. Fentz a, b, *, Mikkel Arendt a, b, Mia S. O'Toole a, b, Asle Hoffart c, d,Esben Hougaard a
a Department of Psychology and Behavioural Sciences, School of Business and Social Sciences, Aarhus University, Bartholins Alle' 9, 8000 Aarhus C, Denmarkb Clinic for Anxiety Disorders and OCD, Aarhus University Hospital, Tretommervej 1, 8240 Risskov, Denmarkc Research Institute, Modum Bad, N-3370, Vikersund, Norwayd Department of Psychology, University of Oslo, Norway
a r t i c l e i n f o
Article history:Received 12 November 2013Received in revised form8 May 2014Accepted 18 June 2014Available online 26 June 2014
Cognitive models of panic disorder (PD) with or without agoraphobia have stressed the role of cata-strophic beliefs of bodily symptoms as a central mediating variable of the efficacy of cognitive behavioraltherapy (CBT). Perceived ability to cope with or control panic attacks, panic self-efficacy, has also beenproposed to play a key role in therapeutic change; however, this cognitive factor has received much lessattention in research. The aim of the present review is to evaluate panic self-efficacy as a mediator oftherapeutic outcome in CBT for PD using descriptive and meta-analytic procedures. We performedsystematic literature searches, and included and evaluated 33 studies according to four criteria forestablishing mediation. Twenty-eight studies, including nine randomized waitlist-controlled studies,showed strong support for CBT improving panic self-efficacy (criterion 1); ten showed an associationbetween change in panic self-efficacy and change in outcome during therapy (criterion 2); three tested,and one established formal statistical mediation of panic self-efficacy (criterion 3); while four tested andthree found change in panic self-efficacy occurring before the reduction of panic severity (criterion 4).Although none of the studies fulfilled all of the four criteria, results provide some support for panic self-efficacy as a mediator of outcome in CBT for PD, generally on par with catastrophic beliefs in thereviewed studies.
Over the last decades, substantial research has demonstratedthat cognitive behavioral therapy (CBT) is an effective treatment forpanic disorder (PD) with or without agoraphobia (e.g. Hofmann &Smits, 2008; Norton & Price, 2007; Stewart & Chambless, 2009).Although CBT's efficacy for PD is well-documented, research onmechanisms of change has been scarce and we know little abouthow and why such treatment works (Kazdin, 2007). Studies onchange processes in psychotherapy most often focus on so-calledmediator variables or mediators. A mediator is an interveningvariable that statistically accounts for the relationship between theindependent variable (e.g. CBT) and the dependent variable (e.g.panic symptom severity; Kazdin, 2007). Establishing statistical
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mediation, however, does not determine whether the mediatingvariable causes therapeutic change. To test a causal relation be-tween mediator and outcome requires establishing a timeline ofchange in the proposedmediator and therapeutic outcome over thecourse of therapy (i.e. that change in the proposed mediator pre-cedes change in the outcome variable). Manipulating the assumedmediators in experimental designs may also prove a causal relationbetween mediator and outcome (Kazdin & Nock, 2003; Kraemer,Wilson, Fairburn, & Agras, 2002). To examine the specificity of aproposed mediator, Kazdin (2007) recommends including alter-native theoretically derived mediators in mediational studies,thereby providing stronger support for the relation between theputative mediator and outcome.
Understanding change processes in CBT for PD is importantsince it can lead to prioritizing effective treatment components andmethods, as well as augmenting treatment for the still large groupof non-responders (Landon & Barlow, 2004). Knowing multiplechange processes could clarify idiosyncratic pathways to change,and lead to more effective, individually tailored treatment.
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Major theories of mechanisms of change in CBT for PD includethe cognitive theories of Beck and Clark (Beck, Emery,& Greenberg,1985; Clark, 1986), and anxiety control theories developed byBarlow (1988). In his widely recognizedmodel of PD, Clark finds themost important factor to be the tendency to catastrophicallymisinterpret innocuous bodily symptoms or mental events (e.g.that a pounding heart may indicate a heart attack; or a feeling ofunreality may mean one is about to lose control or going insane)(Clark, 1997; 1999). These misinterpretations lead to a vicious cycleof escalating anxiety and bodily symptoms, ultimately resulting in apanic attack. CBT for PD disconfirms the catastrophic beliefs andsubstitutes them with more realistic interpretations of the threat-ening stimuli, reducing the intensity of anxiety, and breaking thevicious cycle of panic attacks (e.g. Austin & Richards, 2001; Clarket al., 1999).
Anxiety control theories stress the individual's perceived lack ofcontrol or inability to cope with anxiety-related bodily symptomsand anxiety-provoking situations as an important determinant forthe development and maintenance of PD as well as anxiety disor-ders in general (Barlow, 1988, 2002). Inspired by Lazarus' (1966)appraisal theory, Beck et al. (1985) considered anxiety a result ofboth an appraisal of situations as dangerous, and a perceived lack ofability to cope with the assumed dangers. Casey, Oei, andNewcombe (2004) explicitly applied Beck and Emery's conceptioninto an integrated theoretical model of PD. They find that perceivedlack of ability to cope with panic and catastrophic beliefs aboutdanger play key roles in the development of PD as well as in themediation of therapeutic change in CBT for PD. They refer to theindividual's perceived ability to control or cope with perceiveddangers in relation to panic attacks as “panic self-efficacy” (Casey,Oei, et al, 2004, p. 326). For individuals with PD, perceived dan-gers may comprise both external and internal events. Similarly,panic self-efficacy may include two subdimensions: a) perceivedability to perform a certain action within a feared (agoraphobic)situation, and b) perceived ability to control, discount, or cope withnegative internal states such as feelings of panic, anxiety-relatedbodily symptoms, or negative thoughts (Mineka & Thomas, 1999;Zane & Williams, 1993).
Barlow (1988) suggests that the concepts of perceived controland self-efficacy in relation to panic are overlapping constructs, andthat “it may be possible to extend self-efficacy theory to includeperformance capabilities in dealing with intense anxiety and panic”(p. 298). Bandura's (1988) theory of self-efficacy ascribes a primaryrole to perceived self-efficacy in coping with panic in mediatingpanic symptom reduction, and sees changes in catastrophic beliefsas an effect of change in panic self-efficacy. According to Bandura(1997), perceived self-efficacy may determine whether in-dividuals will initiate appropriate coping behavior in a feared sit-uation rather than safety behavior or avoidance, how hard they willtry, and how long they will sustain their effort in the face of ob-stacles and aversive experiences such as anxiety. Thus, panic self-efficacy seems important for an individual's motivation and will-ingness to engage in challenging new behavior. For instance, itcould lead to a more adaptive interpretation of anxiety-provokingsituations, thereby increasing one's willingness to expose oneselfto them. In therapy, this could be critical in achieving new learningexperiences, reducing the severity of anxiety, and improving theindividual's ability to cope adequately in future similar situations(Bandura, 1997; Bandura & Locke, 2003).
Although, panic self-efficacy or anxiety control has a longtradition in theories of PD etiology and mechanisms of change, ithas been less thoroughly researched than catastrophic beliefs (Oei,Llamas, & Devilly, 1999; Smits, Julian, Rosenfield, & Powers, 2012).No systematic review has yet been published on panic self-efficacyas a mediator in CBT for PD. The present paper defines panic self-
efficacy as perceived ability to cope with or control panic attacks,anxiety-related bodily symptoms, negative thoughts about panic,or agoraphobic situations. We do not address general aspects ofcontrol or self-efficacy, for instance “locus of control” (Rotter, 1966),general self-efficacy (Schwarzer & Jerusalem, 1995), or self-efficacyin relation to other areas.
Aim
The study's primary aim was to conduct a systematic review ofevidence for panic self-efficacy as a potential mediator of thera-peutic outcome in CBT for PD, using both descriptive and quanti-tative (meta-analytic) procedures. We evaluated studies accordingto four criteria often required to establish mediation in an effectivetreatment (Baron & Kenny, 1986; Kraemer et al., 2002). The firstthree criteria were modeled after Baron and Kenny's test of medi-ation (1986) depicted in Fig. 1.
Criterion 1 examines whether the psychotherapeutic interven-tion (CBT) causes change in the proposed mediator (panic self-efficacy; the a path of Fig. 1). Criterion 2 examines the associationbetween change in the proposed mediator and therapeuticoutcome (the b path). Criterion 3 examines formal statisticalmediation. According to Baron and Kenny (1986) this requires (a) areduction of the association between treatment and outcome aftercontrolling for the contribution of the proposedmediator (from c toc’), or (b) as suggested by Sobel (1982), an indirect mediationaleffect as indicated by the interaction of path a and path b. Theo-retically, the indirect, mediated a � b pathway in Sobels's socalled“product of coefficients” approach should correspond to the cminus c’ pathway in the Baron and Kenny “causal steps” approach(Preacher & Hayes, 2008). Criterion 4 examines whether a studyestablishes a causal relation between change in the proposedmediator and change in outcome either by establishing a timeline(mediator precedes outcome) or by experimental manipulation ofthe proposed mediator (Kazdin, 2007; Kraemer et al., 2002). Itshould be noted that mediation is sometimes conditional onmoderator variables (e.g. treatment conditions or patient variables)in which case one may speak of “moderated mediation” (Preacher,Rucker, & Hayes, 2007). A variable may thus function as a mediatorin one treatment condition, but not in another (i.e. moderatedmediation).
Methods
Literature searches
We searched electronic databases (PubMed and PsycINFO)through June 2013, with the following key words in combinationwith panic disorder or agoraphobia: CBT, cognitive behavior therapy,cognitive behaviour therapy, cognitive behavioural therapy, behav-ioral therapy, behavioural therapy, behavior therapy, behaviour ther-apy, exposure, cognitive therapy. Two searches were performed atdifferent times (January and June 2013), one by the first author andone by a research assistant. We checked reference lists from all theincluded papers for additional relevant studies.
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Inclusion criteria
To be included, studies had to investigate change in panic self-efficacy during CBT for adult patients (18 years and older) with aprincipal diagnosis of PD with or without agoraphobia according toa formal diagnostic system, such as the Diagnostic and StatisticalManual of Mental Disorders, Third Edition (American PsychiatricAssociation, 1980) and later editions, or the International Classifi-cation of Diseases, Tenth Revision (World Health Organization,1992). Treatment was considered CBT if it included cognitive (e.g.problem solving skills or cognitive restructuring) or behavioraltreatment methods (e.g. exposure, behavioral experiments,modeling, or social skills training). Only papers published inEnglish-language peer-reviewed journals were evaluated.
Data extraction
The first author (HNF) completed data extraction and the second(MA) checked it with a data extraction sheet. It included verifica-tion of study eligibility, diagnostic criteria used, sample size, age,gender mix, type of treatment condition, number of sessions, in-formation on measures of panic self-efficacy, catastrophic beliefsand outcome measures in the study, statistical procedures, andnumber of participants lost during therapy. Any discrepancies weresolved by consensus.
Analytic strategy of the review
We used meta-analytic syntheses of data to evaluate criteria 1and 2, and qualitatively review on some studies related to criterion2, and all studies related to criteria 3 and 4. None of the studiesrelevant for criterion 3 or 4 reported data necessary for a meta-analysis. In the meta-analyses, results for studies with more thanone active CBT condition, more than one measure of panic self-efficacy, and/or more than one measure of therapeutic outcomewere standardized and summarized so that each study only pro-vided one mean effect size (ES) in the final meta-analysis(Borenstein, Hedges, Higgens, & Rothstein, 2009). When multiplepapers reported findings from the same dataset, we considereddata from the publication providing relevant data. In studies thatalso measured catastrophic beliefs, we compared results for panicself-efficacy with results for this alternative mediator; with regardto criterion 1 only in randomized controlled studies (RCTs).
Related to criterion 1, we calculated a pre-post ES of change inpanic self-efficacy in the form of Cohen's d corrected for the pre-post correlation between measures (Borenstein et al., 2009). Incase no correlation was given or could be calculated (for instance,from t-values), we assumed a correlation of 0.7 as recommended byRosenthal (1993). We also calculated between-group ESs in theform of Cohen's d from RCTs including awaitlist-condition; both forpanic self-efficacy and for the alternative mediator, catastrophicbeliefs. For criterion 2, we calculated the correlation betweenresidualized pre-post change in panic self-efficacy and catastrophicbeliefs, respectively, and residualized change in outcome based onthe Pearson's correlation coefficient (r). Thus, the analyses took intoaccount the pre-therapy level of both the proposed mediators andoutcome variable (Cronbach& Furby, 1979). All ESs were calculatedas weighted means, thus taking number of participants in eachstudy into account.
We conducted meta-analyses using the Comprehensive Meta-Analysis Program, version 2.2.057 (Comprehensive Meta-Analysis,2006; see Borenstein et al., 2009). Analyses were based onrandom-effects models, which yield superior results in terms ofclinical interpretability and external generalizability (Borensteinet al., 2009). Q-statistics evaluated significance of heterogeneity
in the sample of studies (Cochran, 1954), and I2 statistics assessedthe variance accounted for by heterogeneity. I2 values of 25%, 50%and 75% indicate low, moderate, and high degrees of heterogeneity,respectively (Higgins & Thompson, 2002). We checked the risk ofpublication bias, that studies reporting insignificant results orlower ESs are more likely not to be published than studies withhigher ESs, by visually inspecting funnel plots (Light, Singer, Willet,1994) and by means of Egger's test (Egger, Davey, Schneider, &Minder, 1997). A funnel plot is a scatterplot of treatment effectagainst a measure of study size. A skewed funnel plot with a longertail in direction of larger ESs for smaller studies may indicatepublication bias. Egger's test is a formal, statistical analysis of fun-nel plot asymmetry. In case of suggested publication bias, we usedDuval and Tweedie's (2000) trim and fill method to adjust forpossible bias in the overall ES by imputing the ESs of the estimatednumber of missing studies and recalculating the overall ES.Furthermore, Rosenthal's (1991) fail-safeN addressed potential file-drawer problems. If N exceeded 5K þ 10 (K being the number ofstudies included in the meta-analysis), no file-drawer problemwassuspected.
Results
Search results and study characteristics
The flow of information on study selection is summarized inFig. 2. The electronic search strategy yielded 3371 publications.After duplicates were removed, we screened 2664 based on ab-stracts, and evaluated 470 full-texts. Thirty-eight of these fulfilledthe inclusion criteria. We located one more relevant reference(Williams & Rappoport, 1983) from the reference lists of theincluded studies, resulting in 39 eligible studies. We excludedalmost 99% of the identified studies in this broad literature search,59% because the participants had a primary diagnosis other than PDor did not receive CBT. Twenty-two of the 39 eligible studies did notprovide all the data relevant for examining criterion 1 or 2 in themeta-analyses. In these cases we contacted the primary or corre-sponding authors: the authors of 13 studies replied, but only fivesupplied the relevant data. In total, 19 studies provided data forevaluating criterion 1, 7 studies for criteria 1 and 2, one study forcriteria 1, 2 and 3, one study for criteria 2 and 3, one study forcriterion 3, three studies for criterion 4, and one study for criteria 1,2 and 4 (see Table 1). Six of the 39 studies provided insufficientinformation on panic self-efficacy to evaluate any of the fourcriteria and they were therefore not included in the review (Bruce,Spiegel, Gregg,&Nuzzarello, 1995; Feske& Goldstein, 1997; Hoffart& Hedley, 1997; Mackay & Liddell, 1986; Meuret, Seidel, Hofmann,Rosenfield, & Rosenfield, 2012; Williams, Kinney, & Falbo, 1989).Thus, the final number of studies included in the review was 33.
Table 1 summarizes the studies' characteristics. Number ofparticipants varied from 8 to 150 with a total of 1436. Treatmentduration ranged from 3 to 24 sessions with an average of 10.5sessions. The studies used 16 different scales of panic self-efficacy(see the Appendix A that includes an explanation of the abbrevia-tions): the PAI-C (Telch, Brouillard, Telch, Agras, & Taylor, 1989) innine, the SESA (or a shortened version of SESA; Kinney & Williams,1988; Williams, 1990) in six, the ACQ (Rapee et al., 1996) in five, theSE-CPAQ (Gauthier, Bouchard, Cote, Laberge, and French, 1994) infive, the SES (Bandura & Adams, 1977) in three, and the PSEQ(Borden et al., 1991) in three. In nine studies, various measures ofpanic self-efficacy were applied only once. Three studies includedmore than one measure of panic self-efficacy. The scales assesseddifferent aspects of panic self-efficacy: five of the sixteen concernedperceived ability to copewith or control anxiety symptoms or panicattacks, three agoraphobic situations, two both anxiety symptoms
Fig. 2. Flow chart of the study selection.
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and agoraphobic situations, three both agoraphobic situations andscary thoughts, one both anxiety symptoms and scary thoughts,while two included all three aspects of panic self-efficacy: anxietysymptoms, agoraphobic situations, and scary thoughts.
Criterion 1: demonstrating that CBT causes change in panic self-efficacy
Twenty-eight studies provided data for a meta-analysis ofchange in panic self-efficacy from pre- to post-treatment. Theoverall within-group ES for panic self-efficacy was 1.41 (95% CI1.21e1.62; ranging from 0.64 to 2.96) indicating a large ES. Therewas a large between-studies heterogeneity (Q(27) ¼ 154.42,p < .001, I2 ¼ 82.5%). Furthermore, nine out of the ten randomizedcontrolled studies comparing CBT with a waitlist-condition (notKlein & Richards, 2001) provided data for calculating a controlledbetween-group ES for panic self-efficacy. The overall controlled ESwas 1.46 (95% CI 1.08e1.85; ranging from 0.62 to 2.52) in favor ofthe treatment condition. There was a moderate to large between-studies heterogeneity (Q(8) ¼ 24.6, p ¼ .002, I2 ¼ 67.5%). Thesame nine RCTs also provided data on change in catastrophic beliefswith a resulting controlled ES of 1.25 (95% CI 1.66 to 0.83; rangingfrom 0.19 to 2.22). There was a significant moderate to largebetween-studies heterogeneity (Q(8) ¼ 25.9, p ¼ .001, I2 ¼ 69%). Nopublication bias was suspected in any of the analyses. Thus, themeta-analytic evaluations supported that CBT causes a large in-crease in panic self-efficacy, comparable to its decrease in cata-strophic beliefs.
Criterion 2: demonstrating an association between change in panicself-efficacy and outcome
Ten studies provided information on the correlation betweenchange in panic self-efficacy and change in outcome from pre- topost-treatment (Casey, Newcombe, et al., 2005; Casey, Oei, et al.,2005; Cho et al., 2007; Fentz et al., 2013; Feske & de Beuers,1997; Hoffart, 1995b; Williams & Falbo, 1996; Reilly et al., 2005;Schmidt et al., 1997; Van Apeldoorn et al., 2010). The meta-analysis showed a large correlation between improvement of
panic self-efficacy and reductions of panic severity (r ¼ �0.53;CI �0.64 to �0.39; ranging from �0.26 to �0.82). There was a largebetween-studies heterogeneity (Q(9) ¼ 36.5, p < .001, I2 ¼ 75.4%).No file-drawer problem was suspected. However, Egger's testindicated significant asymmetry in the funnel plot (p ¼ .04). Duvaland Tweedie's trim and fill imputation method, adjusting theoverall ES, only reduced the ES marginally (r ¼ �0.47; 95% CI �0.53to �0.40). Nine of the ten studies (not Reilly et al., 2005) alsoprovided information on the correlation between change in panic-related catastrophic beliefs and change in outcome from pre- topost-treatment showing an overall r¼ 0.50 (CI 0.39 to 0.59; rangingfrom r ¼ 0.30e0.71). There was moderate between-studies het-erogeneity (Q(8) ¼ 18.1, p ¼ .021, I2 ¼ 55.7%). No publication biaswas suspected.
In addition, three of the ten studies examined panic self-efficacyand catastrophic beliefs as predictors of panic severity duringtherapy and were also qualitatively evaluated as to criterion 2(Casey, Oei, et al., 2005; Cho et al., 2007; Reilly et al., 2005). Thesestudies examined associations between predictor and criterionvariables by means of either multiple regression analyses orANCOVAs. Cho et al. (2007) simultaneously examined change inpanic self-efficacy, catastrophic beliefs, and anticipated anxiety aspredictors of improvement on four measures of outcome in 120 PDparticipants in the short and long term, immediately after treat-ment and at six-month follow-up (FU). Enhancement in panic self-efficacy during therapy only predicted onemeasure of outcome andonly at short-term, whereas change in catastrophic beliefs andanticipated anxiety both predicted two outcomemeasures at short-term, and three at six-month FU. Reilly et al. (2005) investigatedchange in catastrophic beliefs and three measures of panic self-efficacy as predictors of six outcome measures by means of sepa-rate ANCOVAs. Results indicated that one measure of panic self-efficacy significantly predicted improvement in three out of sixoutcome measures at post-treatment, while the remaining twomeasures of panic self-efficacy predicted improvement in all sixoutcome measures. Change in catastrophic beliefs only predictedchange in two out of six outcomemeasures. Casey, Oei, et al. (2005)investigated working alliance, panic self-efficacy and catastrophicbeliefs as predictors of outcome in three different treatment
Table 1Overview of included studies (N ¼ 33).
Study Total N included/Analyzed
Mean age(SD)/women in %
Treatment (sessions) Panic self-efficacymeasure
Catastrophicbelief measure
Outcome measures(N analyzed/N notincluded in the analyses)
Evaluated criterion 4Borden, Clum, and Salmon (1991) 19/19 23.4 (�)/98.5% PE (10)
CBT (10)PSEQ PACQ PASQ (1/3) 4
Bouchard et al. (2007)(sample identity to Bouchard et al., 1996)
31/12 30.8 (10.9)/92 EXP (15)CR (15)
SEPA AgoCQ-main Panic apprehension (1/9) 4
Fentz et al. (2013) 48/45 39.5 (10.7)/66.7 CBT (14) PAI-C CBS BAI (1/1) 1, 2, 4Hoffart (1998)(sample identity to Hoffart, 1995a)
52/46 40.1 (9.55)/67 CT (15)GMT (15)
S-SESA AgoCQ-physical PDsit, PDspon, IRspon,IRpas, BSQ, PARS1, PARS2,PARS3, MI-ACC, MI-AAL,STAI-Y1, STAI-Y2, BDI,IRGAD, GAS, medicine use,ability to work (17/17)
4
Note: Treatment: BIF: Brief Internet-based treatment, BICT: Brief internet-based cognitive therapy, BT: Bibliotherapy CBT, CART: Capnometry-assisted Respiratory Training, CBT: Cognitive Behavioural Therapy, CBT-brief: sixweeks CBT, CBT comorbid: CBT with a focus on comorbid disorders, CBT-R: CBT with respiratory training, CBT-red: CBT with reduced therapist contact, Comb: Combined treatment, CR: Cognitive restructuring, CT: Cognitivetherapy, EFER: Eye Fixation Exposure and Reprocessing, EMDR: EyeMovement Desensitization and Reprocessing, EXP: Exposure therapy, GMT: GuidedMastery Therapy, ITGIC: Individual Guided Imaginal Coping Therapy, MED:medication, PE: Panic Education (unspecific elements), V-CBT: Videoconference CBT, WL: Waitlist.Measures: The abbreviations for the panic self-efficacy measures, the catastrophic belief measures, and the outcome measuresapplied in the studies are found in Appendix A. Other: FU: Follow-up, RCT: Randomized controlled trial, TPC: telephone contacts.
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conditions. In the first six weeks (Phase 1 of a two-phased treat-ment), all treatment conditions received weekly therapist-administered CBT, after which only two groups continued treat-ment either as usual or computer-administered the last 6 weeks(Phase 2). Hierarchical regression analyses, with working alliance atstep 1, and panic self-efficacy and catastrophic beliefs simulta-neously entered at step 2, demonstrated that changes in panic self-efficacy and catastrophic beliefs significantly contributed to theprediction of panic severity reduction in the first phase of therapy.In the second phase, only change in panic self-efficacy was a sig-nificant predictor of improvement. Working alliance did notsignificantly add to the prediction of panic severity in any of thetreatment phases. The meta-analysis of the ten studies showed alarge negative association between pre-post improvement in panicself-efficacy and reduction in panic severity with comparable ESs asthose found for catastrophic beliefs. Results of the three studiescomparing panic self-efficacy and catastrophic beliefs as predictorsof therapeutic outcome in CBT were more mixed, although resultsalso lended some support for an association between change inpanic self-efficacy and anxiety symptom improvement.
Only three studies reported formal statistical analyses ofmediation. Hoffart (1995b) examined change in panic-self-efficacy,catastrophic beliefs, and perceived control of scary thoughts asmediators of reductions in situational fear in 46 patients randomlyassigned to CBT or Guided Mastery Therapy (GMT; Williams, 1990)in a six-week intensive inpatient program. Hoffart (1995b) assumedcognitive therapy to work through a decrease in catastrophic be-liefs, and GMT through the enhancement of panic self-efficacy. Hisanalysis was thus based on a theoretical hypothesis that mediationwas moderated by therapeutic condition. A multiple regressionanalysis with treatment condition, change in panic-self-efficacy,catastrophic beliefs, and perceived control of scary thoughtsentered simultaneously, revealed that only change in panic self-efficacy significantly predicted situational fear in both treatmentconditions. To test for statistical mediation of change in the twotreatment conditions, interaction terms (mediators � treatmentcondition) were added. None proved significant. Thus, the analysisdid not show a causal relationship between different treatmentsand specific mediators as hypothesized, nor formal mediation bymeans of an interaction effect. The design of the study precludesany conclusion as to panic self-efficacy as a non-specificmediator inboth treatment conditions, since no waitlist control condition wasincluded.
Casey, Newcombe, et al. (2005) examined panic self-efficacy andcatastrophic beliefs as mediators of panic severity in a waitlistcontrol RCT of CBT, including 60 patients with PD. Regression an-alyses indicated that CBT was significantly more effective inreducing panic severity than the waitlist condition, and that bothpanic self-efficacy and catastrophic beliefs changed significantlymore in the treatment condition. Furthermore, both change inpanic self-efficacy and catastrophic beliefs predicted outcome inseparate regression analyses. Finally, when entered simultaneously,together with treatment condition, both proposed mediatorssignificantly contributed to the prediction of outcome, whiletreatment condition did not. Thus, treatment effect was no longersignificant after controlling for the influence of panic self-efficacyand catastrophic beliefs, suggesting that changes in the twocognitive variables fully explained (i.e. mediated) the treatmenteffect.
Meuret et al. (Meuret et al., 2010) used an advanced experi-mental design to directly manipulate proposed mediators; cata-strophic beliefs and respiratory regulation in a comparative study
of five sessions of cognitive training (CT) or respiratory skill training(capnometry-assisted respiratory training, CART) for 47 patientswith PD. Like Hoffart (1995b), their study also primarily investi-gated moderated mediation, since the mediators were hypothe-sized to be differentially involved in the two treatments. Panic self-efficacy was, however, also included as a modality-nonspecificmediator, not directly targeted in the two treatment conditions.In each treatment condition, all proposed mediators were assessedfive times, once at pre-treatment and once at sessions 2, 3, 4, and 5.Longitudinal multilevel modeling with asymmetric distribution ofproducts test for mediation (MacKinnon, 2008), which calculatesthe product of the two segments of the mediated pathway, exam-ined indirect mediated pathways. Results showed no difference inpost-treatment outcome (panic severity) between the two treat-ments. The hypothesized specificity of the two treatmentmediatorswas only partially confirmed; respiratory regulation improvedspecifically during CART while both catastrophic beliefs and panicself-efficacy equally improved in both treatment conditions. Theresearchers tested mediation by including all proposed mediatorssimultaneously and an interaction term between (the product ofpath a and b) in each of the two treatment conditions. Resultsshowed that change in panic self-efficacy mediated change in panicseverity regardless of treatment condition. A reversed relation wasalso seen in both conditions. Change in respiratory regulationmediated change in panic severity only in the CART condition,while catastrophic beliefs mediated reductions in panic severityonly for patients receiving CT, although a bidirectional relationshipwas also found. However, because CT was not proved to specificallycause change in catastrophic beliefs as hypothesized: full statisticalmediation was only found for respiratory regulation in the CARTcondition. As to the role of panic self-efficacy this proposedmodality-nonspecific mediator did mediate panic severity in bothtreatment conditions. However, to fully establish panic self-efficacyas a (nonspecific) mediator of outcome in both CT and CART, awaitlist control conditionwould have been necessary to establish iftreatments did in fact cause the changes in panic self-efficacy (cf.the a path).
Thus, as for criterion 3, three studies tested, but only one study(Casey, Newcombe, et al., 2005) established formal statisticalmediation of panic self-efficacy and catastrophic beliefs in accor-dance with the Baron and Kenny (1986) criteria for mediation.
Criterion 4: causal relation between mediator and outcome
We qualitatively reviewed four studies examining the causalrelation between change in panic self-efficacy and change inoutcome; one study (Hoffart, 1998) by including change in outcomeduring the FU, and three studies (Borden et al., 1991; Bouchardet al., 2007; Fentz et al., 2013) by repeated measurements of theproposed mediators and outcome over the course of therapy.
Based on his aforementioned earlier study (Hoffart, 1995b),Hoffart (1998) examined whether change in panic self-efficacy(measured by S-SESA, a different measure than used in the firstpaper) and catastrophic beliefs during treatment predicted variousoutcome measures at one-year FU. A multiple regression analysisrevealed that change in catastrophic beliefs during therapy pre-dicted change in outcome from post-treatment to FU (residual gainscores) on five of the 17 measures regardless of treatment condi-tion. Panic self-efficacy was not a significant predictor of any of theoutcome measures. Treatment condition (CBT or GMT) had no in-fluence on change in the proposed mediators, rendering a formalmediation test irrelevant according to Baron and Kenny's causalsteps approach to mediation (1986).
Borden et al. (1991) measured panic self-efficacy and level ofpanic symptoms nine times (before treatment, at five weekly
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assessments during treatment, after treatment and at one- andtwo-month FU) in ten sessions of CBT (guided imaginal coping)against non-specific panic education for 19 PD patients. Atime� group ANOVA for the nine assessments of panic self-efficacyrevealed a time effect, but no group or interaction effect, indicatingsimilar change of the variable in both groups. Cross-lagged panelanalyses for the combined treatment group correlated panic self-efficacy and symptoms at subsequent data points. Five of theeight cross-lagged panels indicated changes in panic self-efficacypreceding changes in symptoms; however, most were non-significant and not larger than correlations in the oppositedirection.
Bouchard et al. (2007) investigated panic self-efficacy andcatastrophic beliefs asmediators of change in a study on 15 sessionsof exposure or cognitive restructuring for 12 patients with PD.Participants were recruited from an RCT (N¼ 31) and only includedif they were panic-free after treatment. They filled out daily panicdiaries from the beginning of a six-week pre-treatment self-monitoring period to the end of the six-week post-treatmentperiod, a total of 30 weeks (i.e. > 200 daily observations). The diaryincluded scales from 0 to 100 on the most important catastrophicbelief, self-efficacy in the presence of panic sensations and paniccognitions, respectively, and degree of panic apprehension. Exam-ining individual change trajectories over the course of therapy bymeans of time series analyses (Tiao & Box, 1981) and causalitytesting (Boudjellaba, Dufour, & Roy, 1992) revealed no significantdifferences between the two treatment conditions. Altogether,change in panic self-efficacy predicted subsequent reductions inpanic apprehension in six cases, catastrophic beliefs in three; whileboth of the cognitive variables were involved in three cases.
Fentz et al. (2013) examined change in panic self-efficacy andcatastrophic beliefs as mediators of change in anxiety symptomsmeasured thirteen times during a 13-session group CBT for 46 PDpatients referred to a specialized clinic for anxiety disorders. Datawere analyzed using linear mixed modeling with separation of thebetween- and within-person effects of the proposed mediators.Such a strategymakes amore exact evaluation of thewithin-personchange process of the proposed mediators and outcome duringtherapy possible (Curran & Bauer, 2011). Results revealed a signif-icant treatment effect of both potential mediators and outcomeduring CBT. Multilevel analyses showed that within-personenhancement in panic self-efficacy in a specific session, but not incatastrophic beliefs, preceded within-persons reductions in anxietysymptoms the subsequent week. A significant reversed relationbetween anxiety symptoms and panic self-efficacy indicated areciprocal causal relationship between the variables.
In relation to criterion 4 we found four studies that tested thetemporal precedence of change in panic self-efficacy to outcome.Three of the four studies found change in panic self-efficacyoccurring before the reduction of panic severity. The one studythat tested for a reversed relationship (Fentz et al., 2013) also foundthat prior change in anxiety caused subsequent change in panicself-efficacy.
Discussion
In recent years, the need to investigate mediators of psycho-therapeutic change has been stressed in the scientific field ofclinical research to answer the central question of how specificprocesses or mechanisms underlying therapeutic change work (e.g.Arch, Wolitzky-Taylor, Eifert, & Craske, 2012; Prins & Ollendick,2003). Although more sophisticated analytic strategies and medi-tational designs have been developed (e.g. Bouchard et al., 2007;Meuret et al., 2010), still relatively few studies rigorously examineputative mediators of therapeutic outcome in CBT for PD.
In the present study we sought to review the evidence for panicself-efficacy as a mediator of therapeutic outcome in CBT for PD bymeans of both descriptive and meta-analytic procedures. Our sys-tematic literature search identified 39 studies that investigatedchange in panic self-efficacy during CBT for PD published over thelast 30 years. In relation to Criterion 1, we found strong support forCBT effectively improving panic self-efficacy, as indicated by both alarge pre-post-therapy overall ES (1.41) in twenty-eight studies,and a large between-group ES (d ¼ 1.46) compared to waitlist innine RCTs. Controlled between-group ES for catastrophic beliefs(d ¼ 1.25) in the nine RCTs, although smaller, corresponded to theES for panic self-efficacy. The ten studies related to Criterion 2revealed a large correlation (r ¼ �0.47) between change in panicself-efficacy and change in outcome, similar to that for catastrophicbeliefs (r ¼ 0.50), based on nine of the studies. The three studiesthat examined change in panic self-efficacy and catastrophic beliefsas predictors of therapeutic outcome gave varying results, notclearly favoring one of the two cognitive variables above the other.Only three studies attempted a formal statistical test for mediation(Criterion 3), and only one of these (Casey, Newcombe, et al., 2005)indicated mediation for panic self-efficacy, as well as for cata-strophic beliefs. Finally, four studies were designed to investigatethe causal relation between panic self-efficacy and therapeuticoutcome (cf. Criterion 4). The small, complex study by Hoffart(1995b; 1998) showed mixed results on the role of panic self-efficacy and catastrophic beliefs as mediators in CBT. The threestudies testing temporally precedence of change in the proposedmediators to change in outcome variables during therapy (Bordenet al., 1991; Bouchard et al., 2007; Fentz et al., 2013) all indicatedthat increases in panic self-efficacy preceded subsequent re-ductions of panic severity. Two of the four studies also includedcatastrophic beliefs. Fentz et al. (2013) found that within-personchange in panic self-efficacy, but not in catastrophic beliefs, pre-dicted subsequent within-person change in anxiety symptoms;while Bouchard et al.'s (2007) small, intensive study found indi-vidual trajectories of change over the course of therapy with panicself-efficacy as an independent mediator of outcome in 6 of 12cases while both panic sel-efficacy and catastrophic beliefs medi-ated change in three of 12 cases. Only one study (Fentz et al., 2013)tested and found a bidirectional relationship between panicsymptom severity and panic self-efficacy, not found for cata-strophic beliefs. However, no study using repeated measurementincluded a waitlist-control condition necessary to establish thatCBT drives the change in the proposed mediators during therapy(cf. Criterion 1).
A recent study by Gallagher et al. (Gallagher et al., 2013; pub-lished after the literature search and therefore not included in thereview) also demonstrated temporal precedence of within-personchange in both panic self-efficacy and catastrophic beliefs aboutbodily sensations (i.e. anxiety sensitivity) to within-person reduc-tion in panic symptom severity during an 11-sessions CBT for 361individuals with PD. Results further indicated that the greatestchange in negative thoughts occurred in the first part of treatment,whereas the greatest enhancement of panic self-efficacy occurredin the latter. These results support the assumption that panic self-efficacy and catastrophic beliefs may be independent mediatorsof change in CBT for PD, and indicate that theymay be differentiallyinvolved in different parts of the treatment. That different media-tors may be differentially involved in different phases of treatmentfurther complicates the design of mediator studies.
Overall, none of the studies in this review tested all of thesuggested criteria formediation for panic self-efficacy as amediatorof therapeutic outcome in CBT for PD. There was rather strongevidence that CBT causes change in panic self-efficacy (criterion 1),and that such change is associated with outcome (criterion 2); in
H.N. Fentz et al. / Behaviour Research and Therapy 60 (2014) 23e33 31
both cases of a magnitude comparable to that found for change incatastrophic beliefs. Very few studies focused on formal mediation(criterion 3) or the sequence of change in mediator and outcome(criterion 4), but results here were at least on par with those forcatastrophic beliefs. That none of the studies had designs suitableto test all of the four criteria for mediation is in itself an interestingfinding, given the high priority such studies have been given inmethodological discussions of psychotherapy research, at leastsince year 2000 (e.g. Kazdin & Nock, 2003; Kraemer et al., 2002).
Most of the reviewed studies included both panic self-efficacyand catastrophic beliefs in the analyses, however only threestudies investigated the causal relationship between the two vari-ables over the course of therapy. One study indicated that change inpanic self-efficacy better predicted change in catastrophic beliefsthan vice versa (Borden et al., 1991), Meuret et al. (2010) found nopriority of change in the CBT condition, but temporal precedence oflevel of negative thoughts to later levels of panic self-efficacy in theCARTcondition. Fentz et al. (2013) found no temporal precedence ofany of the two variables over the course of CBT. These few findingsare inconclusive as to the relationship between panic self-efficacyand catastrophic beliefs during CBT. It is thus premature toconclude that one of the variables causes changes in the other - oreven that they both change as a consequence of change in a thirdvariable. Casey, Oei, Newcombe, and Kenardy (2004) have sug-gested that differing results on the association between panic self-efficacy and outcome in CBT research could be explained by thepresence or absence of agoraphobia. Avoidance behavior charac-teristic of patients with agoraphobia may be associated with lowerpanic self-efficacy, and therefore panic self-efficacy may be espe-cially important when agoraphobia is present (see e.g. Cox, Endler,Swinson,& Norton,1992; Telch et al., 1989). It also seems natural tosuppose that the two subdimensions of panic self-efficacy relatedto internal events (panic attacks, anxiety-related bodily symptoms,and negative thoughts) and external ones (feared agoraphobic sit-uations) may be especially relevant to, respectively, PD andagoraphobia. Almost all studies in the review included both typesof participants (i.e. patients with PD with or without agoraphobia),but none reported results separately for the two groups. Thus, thereview cannot throw light on the possible influence of concurrentagoraphobia on panic self-efficacy.
The studies used various types of questionnaires that tappedinto different aspects of panic self-efficacy with about an equalnumber of questionnaires related to each of the suggested sub-dimensions of panic self-efficacy (i.e. internal and external events).The divergence in the conceptualization and operationalization ofthe concept of panic self-efficacy complicates research on itsmediational role. Future research could benefit from a clearerconceptual definition of panic self-efficacy and measurement byuse of the same standardized scales.
The finding that change in panic self-efficacy, as well as changein catastrophic beliefs, are involved in therapeutic change in CBT forPD may have theoretical as well as clinical implications. We pro-pose further integration of so-called positive cognitions concerningperceived ability to control or cope with panic in the cognitivemodels of PD, in line with the integrated model of PD developed byCasey et al (2004a). Our findings could also point to individualtrajectories of change, with panic self-efficacy playing a major rolein some cases, and catastrophic beliefs in others. As indicated byGallagher et al. (2013) the two proposed mediators may be differ-ently involved in different parts of treatment. Although the causalrelationship between the variables is not established by the studies,it seems most likely that they are reciprocally related over thecourse of therapy. Individuals with low perceived ability to copewith panic could thus be more prone to catastrophic mis-interpretations and increased anxiety; or high panic self-efficacy
could help individuals disconfirm the catastrophic beliefs. More-over, individuals with high panic self-efficacy may initiate appro-priate coping behavior to enact more personally valued rather thananxiety-driven actions, and/or be more willing to tolerate andaccept negative states related to anxiety (Borden et al., 1991; Casey,Oei, Newcombe, & Kenardy, 2004; Fentz et al., 2013). Thus, intherapy it may be important to increase the focus on building theindividual's confidence in coping abilities, not only restricted tosituation-specific actions, but also incorporate the individualsperceived ability to handle negative internal states such as bodilysymptoms and scary thoughts. Increased acceptance of negativeinternal states is considered an important therapeutic goal in “thirdwave” therapies like Acceptance and Commitment Therapy (Hayes,Folette, & Linehan, 2004). Paradoxically, a patient with PD couldimprove panic self-efficacy (perceived control) through acceptance(letting go of control) or distancing (‘defusion’) from the internalnegative states such as negative thoughts. Enhanced panic self-efficacy derived from emotion regulation strategies like avoidanceor “over-control” (e.g. inhibition or suppression of negativethoughts and emotions; Gross, 2007) are thus important mal-adaptive coping strategies to address in the treatment of PD.
The present review has several limitations of which some havealready been presented and discussed. Very few studies usedadvanced mediational methodology to examine panic self-efficacyas a mediator of CBT for PD. We could only perform meta-analyseson data for criteria 1 and 2, which are necessary but not sufficientconditions to establish mediation. The data precluded moderatoror subgroup analyses that distinguished participants with orwithout agoraphobia or different measured sub-dimensions ofpanic self-efficacy. The large heterogeneity between studies in allconducted meta-analyses may hinder any firm conclusions. Finally,including various measures of a complex construct like panic self-efficacy could potentially limit the possibility of comparing thestudies.
In conclusion, some support was found for panic self-efficacy asa mediator of therapeutic change in CBT for PD, although none ofthe studies fulfilled all of the four criteria for mediation. Media-tional studies that included both panic self-efficacy and cata-strophic beliefs generally found comparable support for the twoputativemediators. Thus, results may indicate that helping patientsdevelop a higher degree of panic self-efficacy, as well as to examineand change their catastrophic beliefs, could be important in-terventions in CBT for PD. More studies with rigorous mediationdesigns are, however, needed to draw firm conclusions on themediational role of panic self-efficacy on therapeutic change in CBTfor PD.
Acknowledgments
This research work was supported by “Forskningsfonden tilstøtte af psykiatrisk forskning i Region Midt, Denmark” (Researchfoundation in support of psychiatric research in Central Denmark).
Appendix A
Panic self-efficacy measures: ACQ: Anxiety Control Question-naire, PAI-C: Panic Appraisal Inventory - Panic Coping Subscale,PCE: Panic Coping Efficacy, PCSE: Panic Coping Self-efficacy, PSEQ:Panic Self-efficacy Questionnaire, SE-ago: Self-efficacy in agora-phobic situations, SE-CPAQ: Self-efficacy to Control Panic AttacksQuestionnaire, SEP: Self-efficacy in relation to performance, SEPA:Self-efficacy in perceived panic, SES: Self-efficacy Scale, SESA: Self-efficacy Scales for Agoraphobia (normal scale) or S-SESA: shortversion, SEST: Self-efficacy in performing specific tasks, SEQ: Self-efficacy Questionnaire, SEQu: Self-efficacy Questionnaire, SE-
H.N. Fentz et al. / Behaviour Research and Therapy 60 (2014) 23e3332
scales: Self-efficacy scales, SE-thoughts: Self-efficacy in relation tonegative thoughts, SE-Walk: Self-efficacy to walk a given distance.
Catastrophic belief measures: AgoCQ: Agoraphobia CognitionQuestionnaire, AgoCQ-main: Agoraphobia Cognition Questionnairee the individual's main dysfunctional belief, AgoCQ-physical:Agoraphobia Cognition Questionnaire e physical consequencessubscale, ASI/BSQ combined: Anxiety Sensitivity Index and BodySensation Questionnaire combined, BBSIQ: Brief Bodily SensationInterpretations Questionnaire, CBS: Catastrophic Belief Scale, PACQ:Panic Attack Cognition Questionnaire, PAI-conseq: Panic AppraisalInventory e physical consequences subscale, PAI-likelihood: PanicAppraisal Inventory e perceived likelihood of panic attacks.
Outcome measures: AgoCQ-physical: Agoraphobia CognitionQuestionnaire e physical consequences subscale, AgoCQ-social:Agoraphobia Cognition Questionnaire e social consequences sub-scale, API: Acute Panic Inventory, ASI: Anxiety Sensitivity Index,BAI: Beck Anxiety Inventory, BDI: Beck Depression Inventory, BSQ:Body Sensation Questionnaire, FQ: Fear Questionnaire, FQ-Agoraphobia: Fear Questionnaire e agoraphobia subscale, MI:Mobility Inventory, MI-AAL: Mobility Inventory for Agoraphobia-alone, MI-ACC: Mobility Inventory for Agoraphobia-accompanied,Family life: the degree of impairment of family life, Fear of panic:Fear of panic self-monitoring record, GAS: Global Assessment ofFunctioning Scale, HARS: Hamilton Anxiety Rating Scale, HDRS:Hamilton Depression Rating Scale, IRGAD: Interview-rated generalanxiety, IRpas: interview-rated panic symptoms, IRspon:interview-rated spontaneous panic, LOH: Likelihood of harm, Panicfrequency: number of panic attacks during the last week, Panicrecord: Panic frequency self-monitoring record, PARS1: PhobicAvoidance Rating Scale 1 e avoidance of separation, PARS2: PhobicAvoidance Rating Scale 2 e avoidance of social situations, PARS3:Phobic Avoidance Rating Scale 3 e avoidance of simple phobicsituations, PAS; Panic and Agoraphobia Scale, PASQ: Panic AttackSymptoms Questionnaire, Panic thoughts: time spent on negativethinking about panic, PDsit: Panic diary of situational panic attacks,PDspon: Panic diary of spontaneous panic attacks, PDSS: PanicDisorder Severity Scale, SCID-II: the Structured Clinical Interviewfor the DSMeIIIeR personality disorders, SDS: Sheehan DisabilityScale, Social life: the degree of impairment of social life, SPRAS:Sheehan Patient-rated Anxiety Scale, SR-ago: Self-report agora-phobia, STAI: Sheehan Disability Scale, STAI-Y1: State-Trait AnxietyInventory-state, STAI-Y2: State-Trait Anxiety Inventory-trait, TPAR:Texas Panic Attack Record Form,Work: the degree of impairment ofwork.
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