Abstract
Meta-analyses are susceptible to publication bias, the selective publication of studies with statistically significant results. If publication bias is present in psychotherapy research, the efficacy of interventions will likely be overestimated. This study has two aims: (1) investigate whether the application of publication bias methods is warranted in psychotherapy research on posttraumatic stress disorder (PTSD) and (2) investigate the degree and impact of publication bias in meta-analyses of the efficacy of psychotherapeutic treatment for PTSD. A comprehensive literature search was conducted and 26 meta-analyses were eligible for bias assessment. A Monte-Carlo simulation study closely resembling characteristics of the included meta-analyses revealed that statistical power of publication bias tests was generally low. Our results showed that publication bias tests had low statistical power and yielded imprecise estimates corrected for publication bias due to characteristics of the data. We recommend to assess publication bias using multiple publication bias methods, but only include methods that show acceptable performance in a method performance check that researchers first have to conduct themselves.
Highlights
The literature search resulted in 7,647 hits including duplicates, the screening process reduced this number to 502 meta-analyses, of which 89 dealt with the efficacy of psychotherapeutic interventions for posttraumatic stress disorder (PTSD) and were included
One meta-analysis was excluded because it used a network meta-analysis approach (Gerger et al, 2014) and the included publication bias methods cannot be applied to this type of data
Assessing publication bias in any metaanalysis is recommended by guidelines such as Meta-Analysis Reporting Standards (MARS) and PRISMA
Summary
The first goal of this paper is to study whether applying publication bias tests is warranted under conditions that are representative for published meta-analyses on PTSD treatments. We study the statistical properties of publication bias tests by conducting a Monte-Carlo simulation study that closely resembles the meta-analyses on PTSD treatments. The second goal of our study is to assess the severity of publication bias in the meta-analyses published on PTSD treatments. We will not interpret the results of the publication bias tests if it turns out that these tests have low statistical power. Regardless of these results, we will apply multiple methods to correct effect size for publication bias to the meta-analyses on PTSD treatments. Effect size estimates of these methods become less precise (wider confidence intervals), but they still provide relevant insights into whether the effect size estimate becomes closer to zero if publication bias is taken into account
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