Thanks for replying. It runs SAS EG Version 8.3 update 7, so I guess the margins macro isn't included there (yes, it says invocation of the macro is not resolved) . I can't update it or download the macro as it is a government server without internet connection and I don't have administrator rights. However the NLMEANS macro is available and gives the slopes in the 3 month pre and post periods., which is great. I have several more months than I have specified in the table above. I am not quite sure what the all the values in c refer to: pre slope, -.5, 0, .5, 0, 0, 0
post slope, 0, 0, 0, -.5, 0, .5
gap m4-m3, 0, 0, -1, 1, 0, 0 What do these numbers refer to, and how would you adjust if there were e.g. 6 months on each side of the intervention instead of 3?
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