search for: did_dpd

...ossible issue is that I only have 3 time periods, but this should leave me with the first time period to use as an instrument. Below is my full code, along with 4 different pgmm attempts, with 4 different errors. My data is available here if anyone wants to try it: http://dl.dropbox.com/u/3053463/did_dpd.dta Also, likely unrelated, but dynformula has some strange behaviour dynformula(value~value, lag.form=list(value = 1),diff.form=list(TRUE)) Gives: diff(value) ~ diff(diff(value), 1) + diff(value, 1) Where I would have thought it would give this: diff(value) ~ diff(value, 1) Thanks for your time...