I am trying to test for common trends on Stata using coefplot, with 4 dummies for each time period (where they equal 1 at time t and if the individual is in the treatment group).

However, clearly one of the dummies will be omitted during a regression, so how is it possible to see if there's a common trend with only 3 dummy coefficients? Particularly, if common trends did not hold, how could I see whether there are differential trends which could be extracted using triple diff?


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