Statistical analysis
eating disorder
SECONDARY, -11
The first hypothesis, stating that both interventions would be judged acceptable, was tested by calculating the number of sessions attended by the participants in each intervention and the scores on the satisfaction subscales. We also compared the attendance at each intervention and calculated t-tests between the BP group and the HW group to compare the mean scores on the questions of satisfaction.We considered the number of persons who dropped out (i.e. those who did not start the intervention after being randomized or who did not complete the second assessment after having followed one or more sessions of one of the interventions) as an index of feasibility. The BP and HW groups were compared using the chi-squared test. An attrition rate of 10%, found in previous studies with the same interventions [The second hypothesis, that the BP and the HW would improve body dissatisfaction, thin-ideal internalization, dietary restraint, negative affect, and eating disorder psychopathology compared to the WLCG, was tested using per-protocol analyses with a sample of 33 participants. A sample of 90 participants was estimated to be necessary to detect group differences with large effect sizes [The differences in primary and secondary outcomes between pre- and post-assessments for each participant were calculated and then, group comparisons of the difference scores were performed: BP group versus WLCG and HW group versus WLCG, with non-parametric Wilcoxon rank tests. Wilcoxon tests were preferred over standard t-tests to control for departure from normality and homoscedasticity. Due to our small sample size, we decided to interpret our results in terms of effect sizes and not only in terms of To assess the effect sizes of between-group comparisons, the Wilcoxon effect size (The third hypothesis, stating that the effects observed in the intervention groups would be maintained, was tested with non-parametric paired Wilcoxon rank tests, with a systematic comparison of the primary and secondary outcome scores obtained post-intervention and after a one-month follow-up for both interventions. Non-significant differences with small effect sizes were deemed representative of the stability of previously observed effects.Statistical analyses were conducted using IBM SPSS 26 and R version 4.1.2 (2021-11-01).
Participants’ flow diagram throughout the study