You could see if bootstrapping the standard errors via
gives you different results.
You also run a simple t-test to see if there are any differences between the groups
Maybe there are no wage? differences to begin with.
Code:
bootstrap :oaxaca logGRSSWK $wageeq if inlist(DISTYPE,1,4) & quarter == 1, by(DISTYPE) model1(heckman, twostep select($seleq)) model2(heckman, twostep select($seleq)) weight(0) noisily relax
You also run a simple t-test to see if there are any differences between the groups
Code:
ttest logGRSSWK if inlist(DISTYPE,1,4) & quarter==1,by(DISTYPE)
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