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Re: st: Fwd: -cmp- not concave


From   "Z. Liu" <[email protected]>
To   [email protected]
Subject   Re: st: Fwd: -cmp- not concave
Date   Fri, 07 Mar 2014 02:44:00 +0000

Hi DVM,

Many thanks for your kind help. That plus sign is a typo. My apology. It turns out that I made a mistake with the indicators option. I'm redoing the model now. Will also try the -bitobit- command. Thanks a lot.

Best Regards,

Leo


On 2014-03-07 02:30, Dimitriy V. Masterov wrote:
Leo,

Your syntax seems nonstandard to me, particularly the plus sign,
though that doesn't seem to be the problem.

Does the user-written bitobit work by any chance?

DVM

On Thu, Mar 6, 2014 at 5:45 PM, Z. Liu <[email protected]> wrote:
Dear all,

I've been trying to fit a bivariate tobit model using the user-written
command -cmp-. The model looks like this:

cmp (equation1: y1 = X1) (equation2: y2 = y1 + X2), indicators(2 2) robust

This model doesn't work out. Stata keeps showing 'log pseudolikelihood = 0 (not concave)'. I tried to start with minimum regressors (1-2 explanatory
variables) in each equation, but the problem remains. I also tried
alternative ml options such as - tech(dfp)- and -difficult- but still can't
fix it. However, the two tobit equations can be estimated separately,
although the Pseudo R2 is quite small (around 5%). As well, the system model can be estimated if I change the two tobit equations into linear equations. Some descriptive statistics of the two dependent variables are as follows:

y1: Percentiles: 1% (0), 25% (0), 50% (23.57), 99% (6127.14); mean (365.00);
SD (1186.90); Skewness (7.14); Kurtosis (71.23)

y2: Percentiles: 1% (0), 50% (0), 75% (0), 90% (78.10), 99% (1128.53); mean
(61.29); SD (401.82); Skewness (13.27); Kurtosis (217.49)

Anybody out there knows what might be the problem? Any advice or suggestions
would be appreciated. Thanks a lot in advance.


Best Regards,


Leo


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