st: loglikelihood and loglikelihood ratio

[jjc.li@utoronto.ca]

Hi,

I used -sureg- to estimate a system.

1. After using -display e(ll)- to show the loglikelihood, it gives a  
negative value. But I remember I have saw a PPT says loglikelihood is  
a typical negative value. Is mine abnormal?

2. In order to compare unrestricted and restricted models, I used  
-lrtest- to do the loglikelihood ratio test. The LR chi2() value is  
negative.Is it normal? What does it mean? Restricted model better or  
unrestricted model better? If model one LR chi2()=-1, model LR chi2()=  
-10, which one to choose?

3. Is loglikelihood and loglikelihood ratio different? How to display  
loglikelihood ratio in stata?

Thanks!
Jingjing


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