Cognitive-behavioral therapy, such as Heimberg’s CBGT, is an effective intervention for social phobia as already demonstrated in a number of previous studies (Heimberg et al., 1990
; Heimberg, Salzman, Holt, & Blendell, 1993
). Another effective form of intervention is exposure therapy without any explicit cognitive intervention (Feske & Chambless, 1995
; Gould et al., 1997
; Taylor, 1996
). Despite the demonstrated efficacy of these interventions, very little is known about the underlying variables that lead to treatment change (Hofmann, 2000b
). What mediates changes in these treatment modalities, and are those changes unique to a particular type of intervention? The cognitive model of social phobia predicts that estimated social cost is an important mediator of treatment change (Clark & Wells, 1995
; Foa et al., 1996
; Rapee & Heimberg, 1997
). Furthermore, an intervention that specifically targets cognitions to reduce the patients’ overestimation of social cost should be more effective than a treatment that does not directly target cognitions. To test these hypotheses, we compared CBGT, EGT without explicit cognitive interventions, and a wait-list control group in their effects of changes in estimated social cost on changes in social anxiety. We measured estimated social cost with the Foa et al. SCQ (1996)
and applied some of the Kraemer et al. (2002)
recent recommendations to examine mediation.
The two treatments did not significantly differ at posttreatment but were significantly more effective than the wait-list control group. These results are consistent with previous studies that reported no significant differences between exposure therapy and cognitive-behavioral therapy at posttest (Emmelkamp et al., 1985
; Gelernter et al., 1991
; Hope, Heimberg, & Bruch, 1995
; Mattick et al., 1989
; Scholing & Emmelkamp, 1993a
). However, an examination of the effect sizes tends to favor CBGT over EGT in some measures. Specifically, CBGT was associated with a moderate reduction in the SPAI (d
= 0.72) and a large reduction in the SCQ (d
= 0.92) from pre- to posttest. In contrast, EGT was associated with a slightly weaker reduction in the SPAI (d
= 0.52) and only a moderate reduction in SCQ scores (d
= 0.49) from pre-to posttest. Although not statistically significant, slightly more participants prematurely terminated the speech task after EGT (46.7%) than CBGT (33.3%) at posttest. The difference between the treatment groups in self-reported social anxiety became significant at the 6-month follow-up. The effect size of the reduction of SPAI scores from pretest to the 6-month follow-up was 0.68 and 1.55 for the EGT and CBGT group, respectively. These findings support the notion that treatments that are directly aimed at changing dysfunctional cognitions have a more lasting effect on social anxiety (e.g., Butler, 1985
; Butler et al., 1984
; Stopa & Clark, 1993
). It should be noted that the EGT protocol was developed by Stefan G. Hofmann and successfully applied in a number of previous trials (Hofmann, 2000a
; Hofmann et al., 1995
; Newman et al., 1994
). An earlier version of the EGT protocol was further included in three meta-analyses (Feske & Chambless, 1995
; Gould et al., 1997
; Taylor, 1996
), which reported that it was comparable in its efficacy to other interventions, including CBGT. Therefore, experimenter biases, such as expectancy and allegiance effects, are unlikely to explain the outcome of the present study. Nevertheless, the findings of the follow-up data have to be interpreted with caution given the fairly high attrition rate.
Consistent with the proposed mediation model, estimated social cost correlated with treatment choice and had a main effect on outcome in both treatment modalities. These findings support the notion that changes in estimated social cost may be an important mediator of treatment change, as suggested by Clark and Wells’s (1995)
cognitive model of social phobia. To further examine the temporal relationship between changes in estimated social cost and social anxiety, we correlated the pre–post residual gain scores in estimated social cost with the residual gain scores in social anxiety from pretest to the 6-month follow-up assessment. The short-term (pre–post) changes in estimated social cost significantly correlated with the long-term (pre- to 6-month follow-up) changes in social anxiety among individuals receiving CBGT (r
= .60), but not among those receiving EGT (r
= .42). However, the difference between these two correlation coefficients was not statistically significant. These findings suggest that early changes in estimated social cost are associated with later changes in social anxiety among participants receiving CBGT, which is consistent with the proposed mediation model. A similar but smaller effect was found for the EGT group. It should be noted, however, that the number of participants with 6-month follow-up data was relatively small, which might have been the reason why the correlation between pre–post changes in estimated social cost and later changes in social anxiety only reached statistical significance among individuals who received CBGT.
On the basis of these findings, one might hypothesize that repeated exposure to feared social situations in the absence of negative consequences inadvertently forces individuals to reevaluate certain dysfunctional cognitions, including the cognitive biases that lead to the overestimation of social cost. This is consistent with an earlier study that reported changes in cognitions during the course of a behavioral treatment without explicit cognitive strategies (Newman et al., 1994
). Psychotherapy is a complex and interactive process to promote change in clients through means of communication. Therefore, measures of treatment integrity, which only examine the delivery aspect of treatment, are unable to capture the full process of therapy, especially the part of treatment that is actually received by the client. Future studies that compare different treatment modalities should therefore attempt to capture both aspects of therapy.
An important limitation of the present study is related to the nature of the two treatments. The EGT protocol was specifically developed as a treatment for social phobia without any explicit cognitive interventions. However, EGT was not simply a reduced version of the CBGT protocol. In addition to the difference in the emphasis on cognitive strategies, the two protocols also differed in the treatment rationale, which was based on the cognitive model of anxiety in the case of CBGT and on a basic habituation rationale in the case of EGT. Another important limitation is related to the external validity of the results. Some studies suggest that substance use disorder, especially alcohol abuse, may be functionally related to social anxiety in some people (e.g., Carrigan & Randall, 2003
). However, neither of the two therapy protocols provided specific guidelines for the treatment management of those cases. Therefore, similar to other clinical trials (e.g., Heimberg et al., 1998
), individuals with current substance use problems were excluded from the study. Furthermore, only individuals with at least moderate public speaking anxiety were eligible to participate in the study. The majority (89.9%) of all people who presented at the center for treatment were eligible to participate in this study (and reported significant public speaking anxiety). Nevertheless, it remains uncertain whether changes in estimated social cost would have also mediated treatment changes in individuals who were excluded from the study. Further, the study design was less than ideal to examine the temporal precedence criterion of mediation (Kraemer et al., 2002
). Multiple assessments during the course of treatment or even session-by-session assessments of the proposed mediator and the dependent variable would have provided data for a finer analysis of the temporal relationship between these variables. Newer statistical procedures (e.g., hierarchical linear modeling) can examine treatment changes in a combined sample of treatment completers and treatment dropouts when conducting multiple assessments throughout treatment. Finally, there was a small and nonsignificant age difference among the three groups. Participants in the CBGT group tended to be younger than the rest of the sample. However, the effects of the experimental manipulation on the proposed mediator and the dependent variable were not affected when considering age as a possible covariate. Furthermore, age was not a significant covariate in these analyses.
Despite these limitations, this study provides evidence for the role of estimated social cost as a mediator of treatment change in cognitive–behavioral therapy and provides support for the cognitive model of social phobia. Furthermore, the results suggest that cognitive-behavioral therapy leads to more lasting treatment changes than exposure therapy without explicit cognitive interventions, possibly because of the relatively greater influence cognitive–behavioral therapy has on cognitive errors related to overestimation of social cost.