Long time reader, first time poster! I am a clinician trying to improve my statistical knowledge so please forgive me if this is a simplistic question.
I was hoping on some guidance on assessing interactions between groups. Clinical trials and related subgroup analyses often present comparisons between subgroups. In the case of categorical variables such as sex the comparison is made between the groups and a test of interaction performed. This is often also is seen in the literature for continuous variables that are categorised and then compared for interaction. We know there is extensive literature on the issues with dichotomisation/categorisation even if the categorisation is to a clinical used score or staging system.
My first question is, would the more appropriate statistical approach to maximise the power of the data be to keep the variable as continuous and then look at the general interaction of the variable with the intervention of the trial? If this is the better approach, then presumably the variable would need transformation to a normal distribution?