st: Longitudinal modelling of a treatment effect

["Wilson, Ian" <I.Wilson@shu.ac.uk>]

I am undertaking a piece of longitudinal research to identify the 'treatment effect' of a policy initiative.  In textbooks that I have read the suggestion is to use an interaction between time and a dummy for receiving the treatment or not.  In this case since only one interaction variable is included to cover multiple survey waves am I right in thinking that a linear treatment effect has been assumed?

If this is the case could one include a interaction 'dummy' for each survey point in time to capture a more dynamic/non linear 'treatment effect'?



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