Statistical analysis
distress or functional impairment, DSM-5, MPE
SECONDARY
Baseline characteristics of the MPE and SPE groups were compared using descriptive statistics. Number of participants and group percentages are presented for categorical data, with means and standard deviations presented for continuous data. Treatment groups were compared across a number of demographic and service characteristics, and on their baseline scores on the primary and secondary outcome measures.Differences between groups and across time in the scores on the outcome measures were examined using linear mixed-effects models (LMMs). The LMM procedure accommodates both correlated data and unequal variances, and includes both between groups and repeated measures (within-groups) effects at the same time. Participants' scores are deemed to be the result of both fixed effects (e.g. treatment group) and random (e.g. subject) effects, and LMM utilises maximum-likelihood and restricted maximum-likelihood methods to yield optimum estimators (with minimum variance) for balanced and unbalanced designs. Separate LMMs were conducted for each outcome measure. For all measures except for the AQoL-6D, a negative score indicates a reduction in symptoms. For the AQoL-6D a positive score indicates an improvement in quality of life. While not included in the original protocol (Dell et al., Multiple imputation of missing CAPS-5 data at T2 (MPE 15.9%; SPE 26.8%), T3 (MPE 22.2%; SPE 25.4%), and T4 (MPE: 39.7%; SPE: 42.3%) was performed using SPSS with variables in the imputation model chosen if they correlated strongly with CAPS-5 diagnoses being imputed. Imputations were conducted separately for each treatment group to produce 10 imputed datasets. The pooled estimates of the frequencies of CAPS-5 diagnoses were then subjected to χPTSD diagnostic status was determined by dichotomising individual symptoms as ‘present’ or ‘absent’, following the DSM-5 diagnostic algorithm. A symptom was considered present only if the corresponding item severity score was rated 2 (moderate/threshold) or higher. In the CAPS-5, items 9 and 11–20 have the additional requirement of a trauma-relatedness rating of definite or probable, otherwise a symptom is considered absent. The DSM-5 diagnostic rule requires the presence of at least one Criterion B symptom, one Criterion C symptom, two Criterion D symptoms, and two Criterion E symptoms. In addition, Criteria F and G must be met. Criterion F requires that the disturbance has lasted at least 1 month. Criterion G requires that the disturbance causes either clinically significant distress or functional impairment, as indicated by a rating of 2 (moderate) or higher on items 23–25. This calculation of diagnosis is consistent with Voorendonk, De Jongh, Rozendaal, and Van Minnen (Power and sample size were based on the upper endpoint of the 95% confidence interval (CI) for the difference in mean change scores from baseline to 12 weeks between MPE and SPE (adjusted for baseline) being less than the margin of 7 CAPS-5 points, the outcomes of which have been reported elsewhere (Dell et al., All analyses utilised SPSS v27. A 