This is probably very stupid to think about but I am just confused between the difference in adding variables, for example, 'gender', or any group, as a fixed term in regression versus adding the terms as a 'random effect'
Or for example, analysing how weight influenced grip strength between healthy and stroke individuals, should 'healthy vs stroke' be added as a categorical variable or random effect?
In what scenario should I be adding the term categorical or random effect?
