Stefan Elbers

88 Chapter 4 outcome measures (indirectness); or (4) when the total sample size of all included studies was less than the optimal information size of n = 400 (imprecision). We determined the optimal information size with a sample size calculation with α = 0.05, β = 0.8, SD = 0.2 as parameters (Schünneman et al., 2013). To assess publication bias, funnel plot symmetry and distribution of effect sizes were inspected. We based our quality of evidence criteria on the Grade Handbook (Schünneman et al., 2013) and the Cochrane Handbook (Higgins and Green, 2011). RESULTS Study Selection The search yielded 7843 hits. After removal of duplicates and the screening of abstracts, 102 full-text articles were assessed for eligibility. Eighty-two studies were excluded and 20 studies were selected for data extraction and analysis (see Figure 1). Patient and Study Characteristics The total study population consisted of 3557 patients. Seventy-five percent of the study population was female. All studies were performed in Western Europe, Australia or the United States. Average pain duration characteristics were only reported in eight studies and the means ranged from 2.3 to 20 years with a median of 8.4 years. Patient eligibility criteria varied across studies and were based on localization (e.g. back pain), specific diagnosis group (e.g. fibromyalgia syndrome), or duration of pain. Table 1 provides an overview of all participant characteristics within each study. The included studies show substantial variation regarding intervention content, delivery and measurement instruments (table 2). For example, the median number of face-to- face sessions was 6 (range = 3–15), and the median duration was 15 h (range: 2.8–45 h). Furthermore, fifteen studies included a follow-up measurement of at least six months post- intervention, with a mean of 10.53 ( SD = 2.59) months. The mean number of BCTs was 12.6 (range = 5–26). Forty-three of the 93 available BCTs in the taxonomy were identified in the studies and we identified BCTs in all domains of the taxonomy, except for scheduled consequences and covert learning. The domains with the highest numbers of BCTs were goals and planning (accounting for 27.8% of the total BCTs), and social support (10.6%). Six BCTs were frequently used in the interventions: ‘Social support (unspecified) provided by group interventions’, ‘credible source provided by an experienced health care provider or patient’, and ‘goal setting (behaviour)’ were present in at least 90% of the interventions.