I have pre and post measures of the same participants, divided over a Treatment condition and a control condition (no treatment). I have calculated the diff-in-diff by hand and want to know if this is significant.
Therefore, I want to perform a regression with a Treatment dummy (1= treatment, 0=no treatment), a Time dummy (1=post test, 0= prestest) and and the interaction between both. My dependent variable is a math test score.
I know how to create the Treatment dummy. My question is about the Time dummy: Every participant is measured pre and post, so I have 2 columns of math score data in my spss file. I would like to know how to create the Time dummy, as every participant is measured at both times (pre and post).
(I know how to create a dummy variable in spss, but I dont know what the Time dummy should look like).