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st: RE: Prediction after xtpoisson, fe
The prediction is undoubtedly working fine. It is just that what you ask for is not what you want.
I don't know about the fixed effect, but the difference between xb and exp(xb) is a more obvious explanation.
Nick
[email protected]
david reinstein
Following the suggestion of Santos-Silva ("Log of Gravity") I am
regressing a non-negative non-count variable (charitable giving) on a
host of other variables ("price", income etc) using poisson regression
with a fixed effect (admittedly, I have not examined the metrics
behind this procedure extensively, but Wooldridge's 2002 text seems to
also support this):
A simplified version:
> xtpoisson tot_gvg_ lnetincome, fe
I then try to generate predictions (and residuals) for charitable
giving for each (household/year) observation, using (as suggested in
stata help):
> predict psnfexb_tot, xb
But this does not seem to generate reasonable predictions .
Summarizing the data, I get a mean prediction of 1.87, versus a mean
dependent variable of 2092. My guess is it is leaving out the fixed
effect in the prediction.
Any suggestions on how to get this prediction to work? Anyone had
success with this? Thanks.
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