Analysis model assumed at design stage
SE
Let us consider a setting in which a continuous outcome is measured multiple times during follow-up and is modelled using the following random slopes model in the trial analysis:A mixed-effects model such as the one in Eq. (We have introduced the random slopes model in its conditional form, but we can also write it in marginal form. Since our outcome is continuous, the treatment effects and standard errors will be identical from the conditional and marginal formulations, and considering the marginal form allows us to use standard matrix formulae for obtaining the standard error (SE) of the treatment effect. Writing this model in marginal form we get:Standard theory [