I am trying to evaluate a government program where poor schools were selected and given money to improve their infrastructure. I am using results of standardized tests as the outcome variable, and I have a dummy for whether the school received the treatment (aid from government) or not, and I want to compare 2013 results (before treatment) with 2015 results (after treatment)
First, I matched schools considered for aid with their 2013 results, eliminated those that did not match, and created a variable called dummy2013 with a value of one for all.
Second, I matched schools considered for aid with their 2015 results, eliminated those that did not match, and created a variable called dummy2015 with a value of one for all.
Note that most schools matched for both years, but some do not.
Finally, I used the append command to combine the databases and created a dummy called after_dummy, with a value of 1 when dummy2015 was equal to 1 and 0 when dummy2013 was equal to 1. I created the dummy for the interaction and then I run the regression, but stata dropped both the after_dummy variable and the interaction term due to collinearity, what I am doing wrong? How can I solve this?
Thanks a lot in advance.
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