搜索一下啦，stata journal 里有现成的文章介绍的

I think it should be levpet~

OP：findit opreg
LP：findit levpet
Levinsohn, J. and A. Petrin. 2003. Estimating production functions using inputes to control
        for unobservables. Review of Economic Studies 70:  317-342.
Petrin, A., B. P. Poi, and J. Levinsohn. Production function estimation in Stata using
        inputs to control for unobservables. Stata Journal 4(2):  113-123.
Olley, G. S., and A. Pakes. 1996. The dynamics of productivity in the telecommunications
        equipment industry. Econometrica 64: 1263-1297.

good！！！

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