Hi,

I am trying the RESET test (p-value) for a gravity model with fixed effects: (exporter-year, importer-year, pair) as following:
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ppml_panel_sg TRADE RTA if exporter != importer, ex(exporter) im(importer) y(year) cluster(pairid)
estimates store PPMLfesPAIR

***RESET test

predict fit, xb
generate fit2 = fit^2
ppml_panel_sg TRADE RTA fit2 if exporter != importer, ex(exporter) im(importer) y(year) cluster(pairid)
test fit2 = 0
drop fit*
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However, I received this mistake:

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note: fit2 omitted because of collinearity over lhs>0 (creates possible existence issue)
Iterating...





test fit2 = 0
fit2 not found
r(111);

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What should I do?

Thanks!