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st: bitobit estimate


From   Christos Konstantinidis <[email protected]>
To   [email protected]
Subject   st: bitobit estimate
Date   Tue, 15 Mar 2011 18:08:38 +0200

Dear Sir/Madam,
Iam Christos Konstantinidis and I am a Phd Student in the Aristotle University of Thessaloniki, Greece. Within the context of my thesis I use stata for panel data analysis. I have to estimate simultaneously both individually for eight different sectors of food and beverage industry and for the whole sample two equations using the bi-tobit syntax. The employed bi-tobit syntax is the one written by you "bitobit estimate, y1(depvar1) (pnp) y2(depvar2) (ms) x1(varlist) (ms pnplag gr opc ks) x2(varlist) (pnp mslag lev age ks) censor1(varname) (pnp_censor) censor2(varname) (ms_censor)"and the equations have the form below:
pnp=a0+a1ms+a2pnplag+a3gr+a4opc+a5ks
ms=b0+b1pnp+b2mslag+b3lev+b4age+b5ks.
In three of the eight sectors the estimation is ok. However in the rest five sectors as well as in the whole sample the estimation cannot be performed and messages such as ''numerical derivatives are approximate, flat or discontinuous region encountered" or ''could not evaluate numerical derivatives, missing values encountered" appear. Please could you help? Could you also inform me whether the truncated limits have been determined correctly in my syntax? Notice that the dependendent variables, profitability (pnp) and market share (ms) are truncated and take values between -1 and 1 and 0 and 1 respectively.
Thank you in advance.
Christos Konstantinidis


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