Statistical Analysis
pain
SECONDARY
The planned sample size of at least 279 participants (93 in each group) was based on a power of 90% to detect a 4-point mean group difference in MSK-HQ score at 3 months, assuming an SD of 10 points, a correlation of 0.4 between repeated measures in the same participants, 2-sided α = .05, and a 30% study withdrawal rate during follow-up.The primary intention-to-treat analysis estimated mean group differences (with 95% CIs) in MSK-HQ score at 3 months using a constrained longitudinal data analysis approach fit with a linear mixed model.All effect estimates were adjusted for potentially important estimators of the outcome, including age (years), sex (male or female), educational level (<10 years, 10-12 years, or >12 years), and baseline mean pain intensity in the past week (on a scale of 0-10). Preplanned sensitivity analyses of the primary outcome included (1) multiple imputation of missing values using a multivariate normal approach and 20 imputed data sets, (2) complete case analysis including participants with data for all time points, and (3) per-protocol analysis of participants who adhered to the intervention.We estimated the risk ratio for a 4-point or greater improvement in MSK-HQ score from baseline to 3-month follow-up using a Poisson generalized estimated equation (GEE) model. Similar GEE analyses were performed to estimate odds ratios for secondary binary outcomes using a logistic model. All GEE models assumed an exchangeable correlation structure with a robust variance estimator.All estimates of precision were based on 2-sided tests. Statistical significance was defined as 2-tailed 