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From | Scott Merryman <scott.merryman@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: FW: Lambda in Frontier when using uhet |
Date | Mon, 7 May 2012 12:43:16 -0500 |
On Sun, May 6, 2012 at 8:13 PM, Huerta, Tim <tim.huerta@ttu.edu> wrote: > According to Rosko - In developing a preferred model the following > decisions had > to be made: (1) should OLS or SFA be used; (2) what should be the > structural form of the cost function; (3) what theoretical distribution > should the composed error follow; and (4) should inefficiency-effects > variables be included? > > It would seem that when someone is performing an SFE analysis in Stata and > variables are loaded into the uhet, the diagnostic data to answer the > first question isn't provided. In contrast when the uhet is not included, > sigma_v, sigma_u etc. are provided - allowing for the researcher to answer > q1. > > Can someone tell me why including variables in the uhet causes the > information to disappear? Rosko? The information doesn't disappear, but if u is heteroskedastic then there is no lambda, or rather there is a lambda for each observation since sigma_u varies by observation. Before seeing if the frontier model reduces to OLS, test the homoskedasticity restriction that var1-var5 = 0. Scott * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/