Twenty-two studies met these inclusion criteria
+(9,
+10,
+12+–31). Three of these studies examined the effects of both psychodynamic therapy and cognitive behavior therapy
+(9,
+10,
+13). Since there were only three randomized controlled studies for psychodynamic therapy and five for cognitive behavior therapy, we calculated within-group effect sizes for all studies by using Cohen’s d
+(32). For each measure, we subtracted the posttreatment mean from the pretreatment mean and divided the difference by the pretreatment standard deviation of the measure. If there was more than one patient group, we calculated a pooled baseline standard deviation, as suggested by Rosenthal
+(33). If necessary, signs were reversed so that a positive effect size always indicated improvement. Whenever multiple measures were applied in a study, we assessed the effect size for each measure separately and calculated the mean effect size in order to assess the overall outcome of the study. We computed both unweighted effect sizes and effect sizes weighted by the sample size in order to yield unbiased estimators of effect sizes
+(34). Since Cohen’s d gives the amount of change in units of the standard deviation, a standardization of different scalar values of outcome measures is achieved. However, different outcome measures may be more sensitive to change than others (e.g., measures of depression versus measures of personality traits). Thus, the effect sizes of different outcome measures may not be comparable. For this reason, it may be useful to assess effect sizes for certain (classes of) outcome measures separately
+(33). Therefore, we not only computed an overall effect size but also assessed effect sizes separately for measures that were more specific to the core pathology of personality disorders. Furthermore, we assessed effect sizes for self- and observer-rated measures separately, thus taking different observer perspectives into account. If necessary, we used other statistics reported than means and standard deviations (e.g., t or chi-square statistics) to calculate effect sizes
+(32). If studies included patients with and without personality disorders, effect sizes were calculated separately for both groups. There was a problem with the study of Woody et al.
+(13), which pooled the results of the two forms of therapy that were applied. Since the authors found no significant differences between the two forms of therapy applied, we decided to include this study and used the resulting pooled effect sizes as estimates for both forms of therapy. Since the differences between treatments were not significant, no systematic error is implied by this procedure. There was a similar problem with the study of Springer et al.
+(14), which did not report pre- and posttreatment means and standard deviations for the outcome measures. They reported t values of outcome data for the total sample of patients in the therapy and the control condition. Since they did not find significant differences between the therapy and the control condition in outcome measures, we decided to use these data to estimate the effect sizes of the inpatient cognitive behavior therapy condition. We included these studies so as not to reduce the already small number of studies. However, were these studies not included, the results would not change substantially.