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You are dealing with error-specification due to omitted variables. If we take a look in the Stata Reference Manual, we read that:
Omitted variables are a more serious problem than heteroskedasticity or the violations of higher momment conditions
The null hypothesis of the Ramsey test is the lack of omitted variables. Therefore, the way to cope with the issue includes, well, variables. Naturally, modeling must stem from the rationale as well.
Best,
mwai mwai (I do share Joseph's remark about using full names on the list. Thanks).
As an aside to previous helpful insights, some months ago there was an interesting thread on this topic: http://www.statalist.org/forums/foru...-variables-are.
Usually, there is a limited set of measures that you can try (interactions among predictors are included in the list), which are covered in any decent handbook of econometrics.
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