Hello, I am trying to do a simulation analysis to calculate the sample size for a stepped-wedged randomized control trial. The trial is designed such that there are repeated measures (Level 1) of individuals (Level 2) that are nested in clusters (Level 3). I have already defined the number of steps, step length, etc., and I have a number of different input parameters that I want to test (i.e. different numbers of clusters, ICC, and cluster size), but I was wondering if anybody has any experience or reference papers that they can share on how to properly generate the artificial data. The following paper by Heo et al. 2018 is also a three-level model: Sample size determinations for stepped-wedge clinical trials from a three-level data hierarchy perspective. In their paper, they provide the following code: data pvalue; set _NULL_; %do mm = 1 %to &n_sim; do cluster_id = 1 to tot_cluster; do period_id = 1 to tot_period; data one; seed=0; var_y = &sd_y*&sd_y; var_3 = &rho2*var_y; var_2 = (&rho1-&rho2)*var_y; var_e = var_y - var_3 - var_2; tot_cluster = &c*&S; tot_period = &b+&p*&S; u_3 = rannor(seed)*sqrt(var_3); step = ceil(cluster_id/&c); u_2 = rannor(seed)*sqrt(var_2); trt = 1*(period_id > &b+&p*(&S-step)); do sub_id = 1 to &K; end; To help me simulate my own data, can anyone with explain how all the variances terms are calculated (assuming sd =standard deviation, and rho1/2 = level 1 and 2 correlation (i.e. the intraclass correlation))? Additionally, for the random effects terms (u_3, u_2), why did they multiply rannor(seed) by the standard deviation? Many thanks,
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