PSYCHOTHERAPY ENGAGERS VERSUS NON-ENGAGERS

used in the meta-analysis. Since various measures of attachment had been used in the 14
studies, the attachment scores in each study were coded for their degree of approximation
to the two underlying dimensions of attachment avoidance and attachment anxiety. The
mean effect sizes were computed as weighted averages of each samples’ correlation
coefficient, and weights consisted of two coefficients (one for sample size so that each
sample’s contribution to the overall mean would take into account the sample’s size, and
one for weighing samples’ contributions to the overall mean based on how closely they
approximated the constructs of interest; Levy et al., 2011).
Results of Levy et al. indicated that the relationship between attachment anxiety
and psychotherapy outcome (various measures of outcome were used in the various
studies) yielded a Cohen’s weighted d of -0.460, with an 80% credibility interval of d =
-0.320 to -0.608. This indicates that attachment anxiety negatively affects psychotherapy
outcome with a medium effect. The relationship between attachment avoidance and
psychotherapy outcome yielded a Cohen’s weighted d of -0.014, with an 80% credibility
interval d = -0.165 to 0.275. This means that attachment avoidance had little, if any,
effect on psychotherapy outcomes. The relationship between attachment security and
outcome was d = 0.370, with an 80% credibility interval of d = .084 to 0.678. This means
that higher attachment security predicted better psychotherapy outcomes (Levy et al.,
2011).
Limitations of Levy et al. include that treatment type was not controlled for (e.g.,
individual and group therapy were mixed together, long-term and short-term treatments
were combined in the statistical analyses, inpatient and outpatient treatments were
combined), and that there was a lack of pre-treatment baseline data to compare to post-
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