I read everywhere that repeated measures ANOVA is inferior to mixed modelling (since it doesn't handle missing data as well and relies on sphericity assumption). G*Power doesn't tell you how to compute sample sizes for linear mixed models. Should I just do the calculation for RM-ANOVA and go with that number?
My study is: one group takes drug A, another drug B (blinded), surveys with a few continuous questions are given at 5 follow up appointments.
Best Answer
In general, because designs in which linear mixed models are to be used can be complex, it is better to work with a simulation-based approach rather than to rely on specific formulas. If you happen to work in R, you can have a look at the powerlmm package that facilitates this.