Marianne Welmers

Chapter 2 54 Discussion The association between alliance and treatment outcome Our findings revealed a significant small to medium correlation between the level of alliance and treatment outcome ( r = .18), indicating that higher levels of alliance between the therapist and the family lead to more favorable treatment outcomes. This finding is in line with previous meta-analyses on alliance and treatment outcome in youth psychotherapy, showing comparable overall effect sizes, ranging from r = .14 to r = .22 (Karver et al., 2006; McLeod, 2011; Shirk & Karver, 2003; Shirk, Karver, & Brown, 2011) . Meta-analyses on alliance in adult psychotherapy have consistently shown somewhat larger overall effect sizes, ranging from r = .21 to r = .28 (Horvath & Bedi, 2002; Horvath et al., 2011; Martin, Garske, & Davis, 2000). Friedlander et al. (2011) performed a meta- analysis on alliance in couple and family therapy, and found an overall effect size of r = .26 for both couple and family therapy, and an overall effect size of r = .24 for family therapy only. The fact that the present meta-analysis yielded a somewhat smaller overall effect size for family-involved treatment than the meta-analysis by Friedlander et al. (2011) can be explained by several factors. First, we used stricter inclusion criteria for the family aspect of treatment and included unpublished studies as well as published studies. Second, we used a multilevel model instead of a traditional single-level model as used by Friedlander et al. (2011). It can therefore be expected that the present study provides amore accurate estimate of the overall effect size. Furthermore, the previous meta-analysis by Friedlander et al. (2011) did not report an analysis of publication bias, which may have led to an overestimation of the true effect size. In the present study correlations between alliance and treatment outcome reported in studies as non-significant without sufficient data to calculate the true effect size were included, with a conservative estimation of zero. As Rosenthal (1995) pointed out, this conservative estimate of the effect size might lead to an underestimation of the true effect, but simply not using these effect sizes might lead to overestimation of the true effect. To test the hypothesis of underestimation in the present study, we again calculated the overall effect size for the association between the level of alliance and treatment outcome with exclusion of all effect sizes estimated to be zero. The result was a higher overall effect size of r = .22 ( p < .001). However, the Egger and trim and fill analyses indicated that the original overall effect size we found for the association between level of alliance and outcome may still be an overestimation of the true effect size due to publication bias.