Elizabeth said:
Using former posts from Statlist, I've found I need to use the command intreg because a Tobit will not produce robust st. errors.
I want just let you know something related to this issue (althought no Stata code is provided):
Quote from the abstract: "this paper attempts to apply symmetrically trimmed least squares estimation as a semi-parametric estimation of the Tobit model in order to model firms� R&D expenditures with zero values. The result of specification test indicates the semi-parametric estimation outperforms the parametric ML estimation significantly."
Full reference:
Scientometrics, Vol. 69, No. 1 (2006) 57�67
A semi-parametric modeling of firms� R&D expenditures with zero values
SEUNG-HOON YOO & HYE-SEON MOON
Nicola
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