Meta-Analysis of CBT for Anxiety Disorders 1
COGNITIVE-BEHAVIORAL THERAPY FOR ADULT ANXIETY DISORDERS:
A META-ANALYSIS OF RANDOMIZED PLACEBO-CONTROLLED TRIALS
Stefan G. Hofmann, Ph.D.1; Jasper A. J. Smits, Ph.D. 2
1Department of Psychology, Boston University, Boston, Massachusetts
2Department of Psychology, Southern Methodist University, Dallas, Texas
In press: Journal of Clinical Psychiatry
Correspondence concerning the manuscript should be addressed to Stefan G. Hofmann, Ph.D.,
Department of Psychology, Boston University 648 Beacon Street, 6th Fl., Boston, MA 02215,
phone: 617-353-9233; fax: 617-353-9609; e-mail: firstname.lastname@example.org or Jasper A. J. Smits,
Ph.D., Department of Psychology, Southern Methodist University, Dedman College, P.O. Box
750442, Dallas, TX 75275, phone: 214-768-4125; fax: 214-768-3910; e-mail: email@example.com
We thank Angela Berry, Erik Müller, Christiane Suttner, and Kristina Korte for their assistance
with the data extraction, Mark Powers, Ph.D., for his comments on an earlier version of this
manuscript, David Rosenfield, Ph.D. for his statistical advice, and many authors of the original
studies included in these analyses for their valuable support.
Meta-Analysis of CBT for Anxiety Disorders 2
Objective: Cognitive-behavioral therapy (CBT) is frequently used for various adult anxiety
disorders, but there has been no systematic review of randomized placebo-controlled trials. The
present study meta-analytically reviewed the efficacy of CBT versus placebo for adult anxiety
Data Sources: We conducted a computerized search of treatment outcome studies of anxiety
disorders between the 1st available year and March 1, 2007. Furthermore, we examined
reference lists from identified articles and asked international experts to identify eligible studies.
Study Selection: We included studies that randomly assigned adult patients meeting DSM-III-R
or DSM-IV criteria for an anxiety disorder to either CBT or placebo. Of 1,165 studies that were
initially identified, 27 met all inclusion criteria
Data Extraction: The two authors independently identified the eligible studies and selected for
each study the continuous measures of anxiety severity. Dichotomous measures reflecting
treatment response and continuous measures of depression severity were also collected. Data
were extracted separately for completer (25 studies for continuous measures and 21 studies for
response rates) and intent-to-treat analyses (6 studies for continuous measures and 8 studies for
Data Synthesis: There were no significant differences in attrition rates between CBT and
placebo. Random effect models of completer samples yielded a pooled effect size (Hedges’ g) of
0.73 (95% confidence interval, 0.88-1.65) for continuous anxiety severity measures and 0.45
(90% confidence interval, 0.25-0.65) for depressive symptom severity measures. The pooled
odds ratio for completer treatment response rates was 4.06 (95% confidence interval, 2.78-5.92).
The strongest effect sizes were observed for obsessive-compulsive disorder and acute stress
Meta-Analysis of CBT for Anxiety Disorders 3
disorder. The advantage of CBT over placebo did not depend on placebo modality, number of
sessions, or study year.
Conclusions: Our review of randomized placebo-controlled trials indicates that CBT is
efficacious for adult anxiety disorders. There is, however, considerable room for improvement.
Also, more studies need to include intent-to-treat analyses in the future.
Meta-Analysis of CBT for Anxiety Disorders 4
Epidemiological studies indicate that anxiety disorders are the most prevalent class of
mental disorders with a 12-month and lifetime prevalence rates of 18.1% and 28.8%,
respectively 1,2. Numerous studies have examined the efficacy of cognitive-behavioral therapy
(CBT) for adult anxiety disorders. CBT here refers to the class of interventions that are based on
the basic premise that emotional disorders are maintained by cognitive factors, and that
psychological treatment leads to changes in these factors through cognitive (cognitive
restructuring) and behavioral (e.g., exposure, behavioral experiments, relaxation training, social
skills training) techniques 3.
Meta-analytic reviews of these studies have generally yielded large effect sizes for the
majority of treatment studies 4. However, these existing meta-analyses are not without limitations
5,6,7,8,9,10. One of the most concerning weaknesses of meta-analyses involving psychotherapy
research is related to the quality of the original studies. In particular, a number of frequently-
cited meta-analyses of CBT for anxiety disorders have included studies that vary greatly with
respect to control procedures, which range from waitlist, alternative treatments, and placebo
interventions that were evaluated with or without randomization. Other studies fail to include any
control groups 8. Therefore, it has been argued that the results of most existing meta-analyses of
CBT for anxiety disorders are of limited validity because the quality and rigor of meta-analyses
is directly related to the quality and rigor of the studies that are included in these analyses 8,10.
The gold-standard design in clinical outcome research is the randomized placebo-
controlled trial. Although not without problems, this design has been used as the primary test of
the direct effects of the treatment on outcome in clinical research 11. Pharmacotherapy trials
typically administer a sugar pill to individuals in the placebo condition. Instead of including a
Meta-Analysis of CBT for Anxiety Disorders 5
pill placebo, a number of psychotherapy trials have employed psychological placebo conditions
to control for nonspecific factors. Although it is difficult, if not impossible, to protect the blind in
placebo-controlled psychotherapy trials, the randomized placebo-controlled design is still the
most rigorous and conservative test of the effects of an active treatment.
The primary aim of this study was to determine the acute efficacy of CBT as compared to
placebo for adult anxiety disorders. In contrast to existing meta-analyses of CBT for anxiety
disorders, we limited our selection to randomized placebo-controlled trials of DSM-III-R or
DSM-IV anxiety disorders that directly compared the treatment efficacy of CBT with a placebo
condition. We further expanded our search to all types of anxiety disorders in order to compare
the effects of CBT for the various anxiety disorders and explored the potential moderating effects
of number of treatment sessions, placebo modality (pill vs. psychological placebo) and
Several approaches were used to identify studies. First, we searched MEDLINE,
PsycINFO, PubMed, SCOPUS, the Institute of Scientific Information, and Dissertation Abstracts
International. We used the search terms random* in order to identify randomized controlled
studies and we used following terms to identify studies that included a CBT condition: cognitive
behavior* therap*, cognitive therap*, or behavior*therap*. In order to identify studies targeting
specific anxiety disorders, we used the following search terms: GAD, Generalized Anxiety
Disorder, Generalised Anxiety Disorder, OCD, Obsessive Compulsive Disorder, Social Phobia,
Social Anxiety Disorder, Specific Phobia, Simple Phobia, PTSD, Post-traumatic Stress Disorder,
and Acute Stress Disorder. Second, we asked colleagues from Germany, Japan, Korea,
Meta-Analysis of CBT for Anxiety Disorders 6
Netherlands, Portugal, and Spain to identify randomized controlled CBT trials that were
published in their respective languages. Finally, we conducted manual searches in the lists of
references from empirical studies, meta-analyses, and review articles.
SELECTION AND STUDY CHARACTERISTICS
We selected studies that met the following criteria: (1) patients had to be between ages 18
and 65 and met DSM-III-R or DSM-IV diagnostic criteria for an anxiety disorder as determined
by a psychometrically sound and structured diagnostic instrument. Studies with children and
adolescents or geriatric individuals were excluded because the CBT approaches differ greatly
among these age groups. Furthermore, an inspection of the literature suggested that the number
of randomized placebo-controlled studies with children and geriatric samples was insufficient for
a comparison with adult samples 12; (2) patients had to be randomly assigned to either CBT or
placebo. The psychological placebo had to involve interventions to control for nonspecific
factors (e.g., regular contact with a therapist, reasonable rationale for the intervention,
discussions of the psychological problem). Placebo interventions that included active treatment
ingredients for the target problem (e.g., an intervention that specifically instructs participants to
engage in exposure exercises to test certain predictions or to challenge a maladaptive thinking
style) were not included; (3) the clinical severity of the anxiety disorder had to be assessed by
means of psychometrically sound clinician-rated or self-report measures; and (4) reports had to
provide sufficient information to calculate effect sizes (i.e., means and standard deviations, t or F
values, change scores, frequencies, or probability levels)1. Studies that reported on secondary or
sub-analyses of a larger, more complete, or earlier study were excluded from the analysis.
Meta-Analysis of CBT for Anxiety Disorders 7
The two authors independently selected for each study the continuous
interviewer and self-report measures that have shown to be valid and reliable
for the assessment of clinical severity of the anxiety disorder of interest (i.e.,
symptom severity, symptom frequency, and quality of life). For those studies
that reported dichotomous outcomes, we selected the most conservative
measure of treatment response. Measures of depressive symptom severity
were also collected to study the specicity of CBT for the target problem. For
each of these decisions, disagreement between the two authors was
resolved through discussion and consensus was obtained. Two other
individuals independently extracted the numerical data from completer and,
if available, intent-to-treat (ITT; last observation carried forward method)
Eect size estimates of continuous measures
The rst step involved calculating for each study the e&ect sizes for
the di&erence between CBT and placebo. For continuous measures, we
calculated the Hedges’ g e&ect size and its 95% condence interval. This effect
size is a variation on Cohen's d that corrects for biases due to small sample sizes 13 and is
calculated using the following formula:
)1()1( 22 PLACBT
is the mean pre-
to posttreatment change, SD is the standard deviation of posttreatment scores,
is the sample
Meta-Analysis of CBT for Anxiety Disorders 8
size, CBT refers to the CBT condition, and PLA refers to the placebo condition. These controlled
effect sizes may be conservatively interpreted with Cohen’s (1988) convention of small (0.2),
medium (0.5), and large (0.8) effects. We calculated an average Hedges’ g e&ect size
for studies that included multiple continuous measures of anxiety disorder
severity and separate Hedges’ g e&ect sizes for measures of depressive
Effect size estimates of dichotomous measures
For dichotomous measures, we calculated the odds ratio (OR) and its 95% confidence
interval using the Cox–Hinkley–Miettinen–Nurminen method 14. The odds ratio is a measure of
the effect size that is defined as the ratio of the odds of an event (i.e., attrition and treatment
response) occurring in one group (patients in the CBT group) to the ratio of the event in another
group (patients in the placebo condition). Thus, OR was calculated using the following formula:
, where p refers to the percent responders or drop-outs in the CBT
condition and q to the percent responders or drop-outs in the placebo condition. An odds ratio of
1 indicates that the event is equally likely in both groups. If necessary, we reversed signs to
ensure that a positive OR for treatment response indicated an advantage of CBT over placebo.
Pooled effect size estimates
The effect size estimates (Hedges’ g and OR, separately) were combined across studies to
obtain a summary statistic. We adopted random-effects models 15,16 instead of fixed-effects
models, because random-effects models are more appropriate when the aim is to generalize
beyond the observed studies 15. Average effect sizes for the primary outcome measures (i.e.,
anxiety disorder severity, and treatment response) were computed for ITT data in addition to
Meta-Analysis of CBT for Anxiety Disorders 9
It has been argued that meta-analyses may overestimate the overall
e&ect size because studies with non-signicant ndings are often not
published, a bias that is also known as the File Drawer Problem 17. A
conservative method often employed to address this issue involves
calculating the fail-safe N which re4ects the number of unretrieved studies
required to reduce the overall e&ect size to a non-signicant level 18.
According to Rosenthal 19, e&ect sizes are robust if the fail-safe N exceeds 5k +
10, where k re4ects the number of studies included in the meta-analysis. For
the present study, we computed the fail-safe N for the major analyses. All
effect size calculations and publication bias analyses were completed using the program
Comprehensive Meta-Analysis, version 2 20.
To explore the potential impact of study characteristics (study year,
placebo modality) or clinical characteristics (anxiety disorder, number of
treatment sessions) on outcome, we used generalized linear models.
Separate analyses were completed for the e&ect sizes for anxiety and
depression (using data from completer samples). In each analysis, the study
weight was entered as the weight variable and the respective moderator
variable as the factor or covariate. Signicant e&ects of factors were
followed-up with pairwise comparisons using Bonferroni correction.
Meta-Analysis of CBT for Anxiety Disorders 10
Figure 1 presents a flow diagram illustrating the study selection process. Our search
strategy yielded 1,165 potentially eligible studies, of which 27 met all inclusion criteria. Among
the 27 studies, the most commonly studied disorder was social anxiety disorder (SAD; n=7),
followed by posttraumatic stress disorder (PTSD; n= 6), panic disorder (PD; n=5), acute stress
disorder (ASD; n=4), obsessive-compulsive disorder (OCD; n=3), and generalized anxiety
disorder (GAD; n=2). We did not identify any studies that compared CBT to a placebo for the
treatment of specific phobia. Table 1 lists the characteristics for each of the studies included in
the meta-analysis. In order to quantify the quality of the study design, the following scores were
assigned (1 if present; 0 if not) to the clinical trials using modified Jadad criteria 21: (a) The study
was described as randomized; (b) Participants were adequately randomized (e.g., adequate
randomization procedure; the study reported withdrawals and dropouts); (c) Participants and
evaluators were blinded to treatment condition (i.e., participants and evaluators were not aware
whether they received active treatment or placebo intervention); (d) The evaluators were blinded
to treatment conditions (i.e., evaluators were not aware which treatment condition participants
had received; and (e) the description of drop-outs was provided.
Unfortunately, only few studies provided data that was corrected for attrition (i.e., ITT
using last observation carried forward method). Only 6 studies provided ITT data for continuous
measures of anxiety disorder severity from an aggregate of 364 patients (1 study on ASD, 2 on
PTSD, and 3 on PD), and 8 studies (n=524) reported ITT response rates (1 study on ASD, 1 on
GAD, 1 on OCD, 2 on PD, 2 on PTSD and 1 on SAD). Our attempts to obtain ITT data from
authors who did not include these in the original reports were unsuccessful. As shown in Table 1,
25 studies provided completer data for continuous measures of anxiety disorder severity (n =
Meta-Analysis of CBT for Anxiety Disorders 11
1,108). Response rates for completer samples were reported in 21 studies (n=971), and 20
studies provided completer data for measures of depressive symptoms (n=881).
There were no differences in attrition rates between CBT and placebo (OR: 1.19 (95%
CI: 0.88-1.65, z = 1.13, P = .26). The weighted mean attrition rate was 23% for CBT and 22%
for the placebo conditions. The random effects meta-analysis of completer samples yielded mean
effect sizes for the main outcome measures that were in the medium to large range, each
reflecting an advantage of CBT over placebo (see Figures 2 and 3). The overall Hedges’ g for
anxiety disorder severity was 0.73 (95% CI: 0.56-0.90, z = 8.62, P < .001), and the pooled OR
for treatment response was 4.06 (95% CI: 2.78-5.92, z = 7.26, P < .001). As reflected by a mean
Hedges’ g of 0.45 (95% CI: 0.25-0.65, z = 4.52, P < .001) the effect of CBT relative to placebo
on measures of depressive symptom severity was in the small to medium range.
Pooled analyses using data from ITT samples yielded smaller effect sizes. The Hedges’ g
for anxiety disorder severity was 0.33 (95% CI: 0.11-0.54, z = 2.99, P < .001), and the OR for
treatment response was 1.84 (95% CI: 1.17-2.91, z = 2.63, P < .05).
The effect size observed for measures of anxiety disorder severity corresponded to a z-
value of 11.45. Therefore, it would require 829 failed trials for the combined two-tailed p-value
to exceed .05. Fail-safe Ns for the response and measures of depression severity analyses were
411 and 183, respectively. These findings suggest that the effect sizes observed in the present
study are likely to be robust.
Comparison between diagnostic groups
Meta-Analysis of CBT for Anxiety Disorders 12
As can be seen in Figure 4, the effect size for continuous measures of anxiety disorder
severity was largest for OCD (Hedges’ g = 1.37, 95% CI: 0.64-2.20, z = 3.23, P < .001) followed
by ASD (Hedges’ g = 1.31, 95% CI: 0.93-1.69, z = 6.71, P < .001), SAD (Hedges’ g = 0.62, 95%
CI: 0.39-0.86, z = 5.28, P < .001), PTSD (Hedges’ g = 0.62, 95% CI: 0.28-0.96, z = 3.59, P < .
001), GAD (Hedges’ g = 0.51, 95% CI: 0.05-0.97, z = 2.16, P = .03), and PD (Hedges’ g = 0.35,
95% CI: 0.04-0.65, z = 2.24, P = .03). Results of generalized linear models analyses revealed
that the difference among anxiety disorders was significant. (χ2 = 29.31, P < .001). Pairwise
comparisons indicated that the effect size for ASD was significantly greater relative to those
observed for all other disorders with the exception of OCD (all Ps < .05). In addition, the
difference between OCD and PD was significant (P < .05).
Differences in Hedges’ g for measures of depressive symptom severity among anxiety
disorders were not significant (χ2=3.78, P=.58; see Figure 4). Significant effect sizes were
observed for PTSD (Hedges’ g = 0.59, 95% CI: 0.20-0.98, z = 2.97, P < .001) and OCD (Hedges’
g = 0.34, 95% CI: 0.04-0.65, z = 2.19, P = .03). Effects sizes approached significance for ASD
(Hedges’ g = 0.32, 95% CI: -0.03-0.66, z = 1.79, P = .07) and SAD (Hedges’ g = 0.66, 95% CI:
-0.10-1.42, z = 1.42, P = .09). Non-significant effect sizes were observed for GAD (Hedges’ g =
0.38, 95% CI: -0.23-0.98, z = 1.22, P = .22) and PD (Hedges’ g = 0.14, 95% CI: -0.21-0.49, z =
0.78, P = .43).
A comparison of the odds ratios of treatment response showed a similar pattern of results.
As shown in Figure 5, the largest odds ratio was observed for OCD (OR = 12.24, 95% CI: 2.91-
51.55, z = 3.42, P < .001) and ASD (OR = 8.07, 95% CI: 1.96-33.21, z = 2.89, P < .001),
followed by SAD (OR = 4.21, 95% CI: 2.07-8.98, z = 3.90, P < .001), PTSD (OR = 3.06, 95%
CI: 1.54-6.07, z = 3.19, P<.001), and PD (OR = 2.52, 95% CI: 1.18-5.39, z = 2.38, P < .002).
Meta-Analysis of CBT for Anxiety Disorders 13
The odds ratio did not reach statistical significance for GAD (OR = 2.27, 95% CI: 0.49-10.56, z
= 1.04, P = .03).
The Hedges’ g for anxiety disorder severity was not moderated by the number of sessions
(B = -.02, SE = .02, P = .47), publication year (B = .02, SE = .02, P = .37), or placebo modality
(i.e., psychological vs. pill placebo; B = 0.14, SE = .20, P = .46) Similarly, the effect sizes for
continuous measures of depression symptom severity did not depend on the number of sessions
(B = 0.24, SE = .03, P = .41), publication year (B= -0.13, SE = .02, P = .59), or placebo modality
(B = 0.21, SE = .26, P = .42).
A number of meta-analyses support the efficacy of CBT for anxiety disorders. However,
existing meta-analyses of CBT have focused on only one or a few selected disorders and
included a heterogeneous number of studies ranging from randomized, placebo-controlled trials
to small uncontrolled, open-label studies. This led some authors to question the validity of the
findings from these analyses 8. Limiting a meta-analysis to only randomized placebo-controlled
studies circumvents some of these methodological problems.
The goal of the present study was to estimate the efficacy of CBT compared to
psychological or pharmacological placebo conditions, to compare the efficacy of CBT for DSM-
III-R or DSM-IV anxiety disorders, and to examine whether then number of treatment sessions,
the placebo modality, and publication year moderates treatment outcome. To answer these
questions, we screened 1,165 studies and identified 27 randomized placebo-controlled trials
totaling 1,496 patients. As reflected by medium to large effect sizes for measures of anxiety
disorder severity, CBT yields significantly greater benefits than placebo treatments. The results
Meta-Analysis of CBT for Anxiety Disorders 14
revealed that the effects were significantly greater for ASD relative to all other disorders with
exception of OCD. Moreover, CBT for OCD was more effective than CBT for PD. This pattern
of result is somewhat surprising and runs counter the general notion that OCD is the most
treatment-resistant anxiety disorder. Obviously, a strong effect size based on a large number of
patients in clinical trials does not rule out the possibility of encountering a highly treatment
resistant case in clinical practice. This disjunction between clinical experience and empirical data
may be particularly evident in disorders with a wide range of symptomatology and severity, as is
the case in OCD-spectrum disorders.
The overall effect size findings are generally in line with more recent meta-analyses that
only examined single disorders using considerably less stringent inclusion criteria for the original
studies 90,91,92,93,94.These studies reported effect sizes for CBT that were in the medium to large
range. Moreover, we observed no difference between the pill placebo and the psychological
placebo condition, and the psychological placebo conditions were structurally equivalent to the
respective CBT intervention. Therefore, it is unlikely that the effect sizes found in the present
study were systematically biased by the choice or the structure and duration of the placebo
control condition 95. Finally, the publication bias is unlikely to account for the observed effects.
In order to examine the specificity of the CBT intervention for reducing anxiety, we
explored the treatment effects on depression in addition to the targeted anxiety disorder. We
chose to examine the effects on depression because of the high comorbidity between anxiety and
depression, and because CBT for anxiety disorders was originally derived from the CBT
approach for depression. Although the pooled effect size was statistically significant (Hedges’ g
= 0.45, P<.001), a comparison between CBT and placebo by the diagnostic groups showed that
Meta-Analysis of CBT for Anxiety Disorders 15
CBT only significantly outperformed placebo in reducing depression in PTSD and OCD. These
findings support the specificity of CBT for most of the anxiety disorders
Although we avoided many of the potential methodological problems of meta-analytic
studies, there remain a number of notable weaknesses. First, although the majority of studies that
were included in the analyses were of generally high quality as assessed by the Jadad criteria21, a
surprisingly large number of these studies failed to report ITT data. Despite our attempts to
obtain these data from the investigators, it was not possible to gather enough information to
compare the ITT effect sizes between the specific anxiety disorders. The pooled ITT effect size
for continuous anxiety severity measures and the OR for treatment response were small (Hedges’
g = 0.33; OR: 1.84), but statistically significant. Because of the small number of studies, the
results of these analyses should be interpreted with caution (6 studies for the analyses of the
continuous measures and 8 studies for the dichotomous response rate estimate). It is, however,
surprising that the completer analyses yielded greater effect sizes than the ITT analyses. The
dropout rates in CBT were relatively small and, therefore, are unlikely to account for this
difference. A plausible explanation is the fact that the ITT analyses included mostly studies with
panic disorder samples, which in the completer analyses were associated with relatively small
effect sizes (see Figure 4).
Despite recent findings indicating that effects sizes for ITT samples may not differ from
those observed with completer samples 93, it is quite possible that the effect sizes of the
completer analyses are biased. Given the status of CBT as the gold-standard psychosocial
intervention for treating anxiety disorders, it is very surprising and concerning that after more
than 20 years of CBT treatment research, we were only able to identify 6 high-quality
randomized placebo-controlled CBT trials that provided ITT analyses for continuous measures
Meta-Analysis of CBT for Anxiety Disorders 16
and only 8 trials for ITT response rate analyses. In our opinion, this is an unacceptable situation
that will have to change for psychosocial intervention to become a viable alternative to
pharmacotherapy in the medical community.
Second, most of the trials that were selected also included combined treatment
conditions, such as a combination between CBT and pharmacotherapy, or a combination between
CBT and pill placebo. These conditions were not included in the present analyses because the
objective of this study was to only examine the efficacy of CBT as monotherapy as compared to
placebo as monotherapy. Third, CBT refers to a family of interventions that share the basic
therapeutic principles and treatment rationale. However, the specific treatment techniques and
emphasis on the various treatment components differ from disorder to disorder. These differences
might have accounted for some of the differences in treatment efficacy. Similarly, there was
some variation in the nature of the placebo conditions, and it is possible that some placebo
conditions were more efficacious than others. However, we did not find any systematic
differences between the trials in placebo conditions, and there was no difference between
psychological and pill placebos. Finally, although we limited the diagnoses to DSM-III-R and
DSM-IV criteria, we were unable to estimate the effect sizes of panic disorder with agoraphobia
separate from panic disorder without agoraphobia because most of the clinical trials on panic
disorder did not distinguish these two diagnostic groups.
Despite these weaknesses, our quantitative literature review of randomized placebo-
controlled trials provides strong support for the efficacy of CBT as an acute intervention for adult
anxiety disorders. At the same time, the results also suggest that there is still considerable room
for further improvement. As suggested by recent findings, pharmacological augmentation
Meta-Analysis of CBT for Anxiety Disorders 17
strategies designed to enhance the learning that occurs with CBT approaches for anxiety
disorders may hold particular promise 96,97.
Meta-Analysis of CBT for Anxiety Disorders 18
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Table 1: Characteristics of Studies Included in the Meta-analysis.
al., 1998 22
ASD CBT Supportive
24 5 IES BDI Completer 1
al., 1999 25
ASD CBT Supportive
38 6 IES BDI Completer 2
al., 2003 26
ASD CBT Supportive
24 5 IES BDI Completer 3
al., 2005 27
ASD CBT Supportive
57 6 IES BDI Completer,
GAD CBT Nondirective
43 12 HAM-A,
BDI; HAM-D Completer 2
et al., 2003
GAD CBT Discussion
52 12 ADIS-IV
BDI; HAM-D Completer 2
Foa et al.,
OCD ERP Pill Placebo 55 15 CGI-S,
al., 2002 41
OCD BT Systematic
167 10 YBOCS,
HAM-D Completer 1
al., 1997 45
OCD ERP Anxiety
18 15 YBOCS,
BDI Completer 1
al., 1999 46
PD CT Pill Placebo 67 12 CGI-S,
al., 2000 49
PD CBT Pill Placebo 101 12 PDSS Completer,
Black et al.,
PD CT Pill Placebo 50 8 CGI-S, CAS,
al., 1995 53
PD CBT Nondirective-
30 4 ADIS-R –
Sharp et al.,
PD CBT Pill Placebo 80 10 MADRS ITT 2
et al., 2003
PTSD CBT Supportive
73 12 CAPS-2, BSI,
BDI Completer 2
al., 2003 63
PTSD CBT Supportive
38 8 CAPS-2, IES,
BDI Completer 3
Foa et al.,
PTSD PE Supportive
28 9 PTSD
BDI Completer 2
al., 1998 67
PTSD CBT Relaxation 45 10 PTSD
BDI Completer 2
et al., 2005
PTSD CBT Problem-
51 14 CAPS-2,
al., 2004 70
PTSD NET Supportive
31 4 PDS, MOS Completer 2
Clark et al.,
SAD CT Pill Placebo 43 16 ADIS-
BDI Completer 2
al., 2000 77
SAD CBT Supportive
63 8 LSAS, QOL,
BDI Completer 3
al., 2004 79
SAD CCBT Pill Placebo 120 14 CGI-S, BSPS,
et al., 1998
SAD CBGT Educational
69 12 ADIS-R-
SAD CBGT Educational-
44 12 SPAI; SIAS;
BDI Completer 2
Smits et al.,
SAD BT Psychological
38 3 LSAS-SR,
al., 1994 88
SAD BT Pill Placebo 47 20 Completer 2
Note: ASD = Acute Stress Disorder; GAD = Generalized Anxiety Disorder; OCD = Obsessive Compulsive Disorder; PD = Panic Disorder; PTSD =
Post Traumatic Stress Disorder; SAD = Social Anxiety Disorder. BT = Behavior Therapy; CT = Cognitive Therapy; CBGT = Cognitive-Behavioral
Group Therapy; CBT = Cognitive-Behavioral Therapy; CCBT = Comprehensive Cognitive-Behavioral Therapy; ERP = Exposure and Response
Prevention; NET = Narrative Exposure Therapy; PE = Prolonged Exposure. ADIS-IV = Anxiety Disorder Interview Schedule for DSM-IV 36; ADIS-R
= Anxiety Disorder Interview Schedule Revised 30; ASI = Anxiety Sensitivity Index 54; BAI = Beck Anxiety Inventory 37; BDI = Beck Depression
Inventory 24; BSI = Brief Symptom Inventory 60; BSPS = Brief Social Phobia Scale 80; CAPS-2 = Clinician Administered PTSD Scale, version 2 59;
CAS = Clinical Anxiety Scale 52; CCQ = Catastrophic Cognitions Questionnaire 64; CGI - S = Clinical Global Impressions Scale – Severity 39; FDAS =
Four Dimensional Anxiety Scale 56; FNE = Fear of Negative Evaluation Scale 76; FQ = Fear Questionnaire 55; FQ – SP = Fear Questionnaire – Social
Phobia scale 55; HAM-A = Hamilton Anxiety Rating Scale 29; HAM – D = Hamilton Depression Rating Scale 31; IES = Impact of Event Scale 23; LIFE =
The LIFE Base 61; LSAS = Liebowitz Social Anxiety Scale 75; LSAS-SR = Liebowitz Social Anxiety Scale – Self Report 87; MADRS = Montgomery-
Asberg Depression Rating Scale 48; MOCI = Maudsley Obsessional-Compulsive Inventory 44; MSPS = Marks-Sheehan Phobia Scale 47; PADUA = The
Padua Inventory 43; PCL = PTSD Checklist 62; PDS = Post-traumatic Stress Diagnostic Scale71; PDSS = Panic Disorder Severity Scale 50; PGE = Patient
Global Evaluation 47; PSWQ = Penn State Worry Questionnaire 34; PTSD symptom scale = Post-traumatic Stress Disorder Symptom Scale66; QOL =
Quality of Life scale 77; QOLI = Quality of Life Index 69; SAD = Social Avoidance and Distress Scale 76; SCL – 90-R-Depression = Symptom Checklist
90 Revised – Depression 84; SCL – 90-R-IS = Symptom Checklist 90 Revised – Interpersonal Sensitivity 84; SCL-90- PA = Symptom Checklist 90
Revised – Phobic Anxiety 84, SDS = Sheehan Disability Scale 47; SIAS = Social Interaction Anxiety Scale 74; SISST = Social Interaction Self-Statement
Test 78; SPAI = Social Phobia Anxiety Inventory 81; SPDS-S = Social Phobic Disorder Severity and Change Form – Severity 83; SPS = Social Phobia
Scale 74; SPWSS = Social Phobia Weekly Summary Scale 73; SRT = Symptom Rating Test72; STAI-T = State Trait Anxiety Inventory – Trait subscale 32;
WSAS = Work and Social Adjustment Scale 42; YBOCS = Yale Brown Obsessive Compulsive Scale 40; ZSRA = Zung Self-Rating of Anxiety Scale 33.
Figure 1: Study selection and reasons for exclusions.
Figure 2: Effect size estimates (Hedges’ g) and the statistical tests of the acute treatment efficacy of CBT compared to placebo
on the primary continuous anxiety measures for the identified studies.
Study Name Statistics for each study Hedges's g and 95% CI
Hedges's Lower Upper
g limit limit Z-Value p-Value
ASD - Bryant et al. (1998) Combined 1.49 0.60 2.38 3.29 0.00
ASD - Bryant et al. (1999) Combined 1.28 0.52 2.04 3.29 0.00
ASD - Bryant et al. (2003a) Combined 1.66 0.75 2.58 3.57 0.00
ASD - Bryant et al. (2005) Combined 1.08 0.47 1.69 3.47 0.00
GAD - Borkovec & Costello (1993) Combined 0.57 -0.08 1.21 1.71 0.09
GAD - Wethrell et al. (2003) Combined 0.44 -0.21 1.10 1.34 0.18
OCD - Foa et al. (2005) Combined 1.65 0.95 2.35 4.62 0.00
OCD - Greist et al. (2002) Combined 0.74 0.40 1.08 4.32 0.00
OCD - Lindsay et al. (1997) Combined 2.08 0.91 3.26 3.48 0.00
PD - Bakker et al. (1999) Combined 0.43 -0.09 0.96 1.62 0.11
PD - Barlow et al. (2000) PDSS 0.23 -0.35 0.81 0.77 0.44
PD - Black et al . (1993) Combined 0.26 -0.40 0.92 0.78 0.44
PD - Craske et al. (1995) Combined 0.49 -0.25 1.22 1.29 0.20
PTSD - Blanchard et al. (2003) Combined 0.65 0.11 1.20 2.35 0.02
PTSD - Bryant et al. (2003b) Combined 1.48 0.68 2.29 3.61 0.00
PTSD - Foa et al. (1991) Combi ned 0.44 -0.39 1.28 1.05 0.30
PTSD - Marks et al. (1998) Combined 0.75 0.11 1.40 2.28 0.02
PTSD - McDonagh et al. (2005) Combined 0.13 -0.50 0.77 0.41 0.68
PTSD - Neuner et al. (2004) Combined 0.41 -0.32 1.14 1.10 0.27
SAD - Clark et al. (2003) Combi ned 0.89 0.25 1.53 2.72 0.01
SAD - Cottreaux et al. (2000) Combined 0.51 -0.02 1.04 1.89 0.06
SAD - Davidson et al. (2004) Combined 0.52 0.09 0.96 2.36 0.02
SAD - Heimberg et al. (1998) Combined 0.94 0.36 1.52 3.15 0.00
SAD - Lucas (1994) Combined 0.43 -0.23 1.09 1.28 0.20
SAD - Smits et al. (2006) Combined 0.53 -0.15 1.21 1.52 0.13
0.73 0.56 0.90 8.62 0.00
-4.00 -2.00 0.00 2.00 4.00
Favors PLA Favors CBT
Note: ASD = Acute Stress Disorder; GAD = Generalized Anxiety Disorder; OCD = Obsessive-
Compulsive Disorder; PD = Panic Disorder; PTSD = Post Traumatic Stress Disorder; SAD = Social
Figure 3: Odds ratios and statistical tests of the acute treatment response to CBT versus placebo for the identified studies.
Study name Outcome Statistics for each study Odds ratio and 95% CI
Odds Lower Upper
ratio limit l imit Z-Valuep-Value
ASD - Bryant et al. (1998) CIDI = No PTSD Diagnosis 55.00 4.30 703.43 3.08 0.00
ASD - Bryant et al. (1999) CAPS2 = No PTSD Diagnosis 8.00 1.33 48.18 2.27 0.02
ASD - Bryant et al. (2003a) CAPS2 = No PTSD Diagnosis 15.40 1.47 160.97 2.28 0.02
ASD - Bryant et al. (2005) CAPS2 = No PTSD Diagnosis 2.02 0.62 6.55 1.17 0.24
GAD - Brokovec & Costello (1993) 6 Outcome Measures > 20% Improvement 4.81 1.14 20.25 2.14 0.03
GAD - Wetherell et al. (2003) 3 Outcome Measures > 20% Improvement 1.00 0.21 4.81 0.00 1.00
OCD - Foa et al. (2005) CGI-I = 1 53.95 2.88 1009.80 2.67 0.01
OCD - Greist et al. (2002) CGI-I < 3 8.52 3.83 18.96 5.25 0.00
PD - Barlow et al. (2000) CGI-I < 3 and CGI-S <4 1.67 0.48 5.81 0.80 0.42
PD - Black et al. (1993) CGI-I < 3 3.47 0.73 16.53 1.56 0.12
PD - Sharp et al. (1996) SRT = CCS 3.07 0.91 10.30 1.81 0.07
PTSD - Blanchard et al. (2003) CAPS2 = No PTSD Diagnosis 3.77 1.16 12.27 2.20 0.03
PTSD - Bryant et al. (2003b) CAPS2 = No PTSD Diagnosis 9.75 1.59 59.70 2.46 0.01
PTSD - Foa et al. (1991) PTSD Symptom Scale = CCS 2.67 0.36 19.71 0.96 0.34
PTSD - McDonagh et al. (2005) CAPS2 = No PTSD Diagnosis 1.65 0.44 6.20 0.74 0.46
PTSD - Neuner et al. (2004) SRQ-20 > 10 2.00 0.30 13.26 0.72 0.47
SAD - Davidson et al. (2004) CGI-I < 3 2.55 1.05 6.21 2.07 0.04
SAD - Heimberg et al. (1998) SPDS-S <3 and SPDS-C <3 5.67 1.75 18.38 2.89 0.00
SAD - Lucas (1994) 2 Outcome Measures = RC 2.33 0.48 11.40 1.05 0.30
SAD - Smits et al. (2006) LSAS-SR > 50% Improvement 12.63 0.64 250.04 1.66 0.10
SAD - Turner et al. (1994) CGI-I < 3 25.33 2.84 226.07 2.89 0.00
4.00 2.94 5.44 8.80 0.00
0.01 0.1 1 10 100
Favors Placebo Favors CBT
Note: CIDI = Composite International Diagnostic Interview; CAPS-2 = Clinician Administered PTSD
Scale, version 2 59; CGI - S = Clinical Global Impressions Scale – Improvement 39; SRT = Symptom Rating
Test72; PTSD symptom scale = Post-traumatic Stress Disorder Symptom Scale66; SPDS-S = Social Phobic
Disorder Severity and Change Form – Severity 83; LSAS-SR = Liebowitz Social Anxiety Scale – Self Report
87; CSS = Clinically Significant Change97; RC = Reliable Change97.
Figure 4: Average effect size estimates (Hedges’ g) and corresponding 95% confidence intervals of the acute treatment efficacy
of CBT as compared to placebo on the various anxiety disorders for the primary continuous anxiety measures (red bars) and
depression measures (green bars).
Effect Size (Hedges' g)
0.0 0.5 1.0 1.5 2.0 2.5
Generalized Anxiety Dis.
Social Anxiety Dis.
Post-traumatic Stress Dis.
Acute Stress Dis.
Figure 5: Average odds ratios of acute treatment response to CBT as compared to placebo and statistical tests for the various
anxiety disorders. *: P < .05; **; P < .001
0 2 4 6 8 10 12 14
Generalized Anxiety Dis.
Social Anxiety Dis.
Post-traumatic Stress Dis.
Acute Stress Dis.