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From |
"sdm1" <[email protected]> |

To |
<[email protected]> |

Subject |
st: RE: Not Directly Stata Related, But Please Help |

Date |
Wed, 12 Mar 2008 23:39:03 -0000 |

```
Victor,
I have no problem with you posting here but why not email your question to
one or both of the authors?
Steve
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Victor Waters
Sent: 12 March 2008 22:55
To: [email protected]
Subject: st: Not Directly Stata Related, But Please Help
Apologies for question not directly related to STATA.
If you think I should not have posted this here, please tell me where to
ask. Thanks
My question is about deriving a formula in Cameron and Trivedi
Microeconometrics 2005.
On page 763 the following equations and text appears.
-------------------------
y_it = gamma y_i,t-1 + alpha_i + epsilon_it, i = 1 to N, t=2, .. T
Cor(y_it, y_i,t-1) = Cor [gamma y_i,t-1 + alpha_i + epsilon_it, y_i,t-1]
= gamma + Cor [ alpha_i , y_i,t-1]
= gamma + (1- gamma) / 1 + (1- gamma) sigma_epsilon ^2 / (1 + gamma)
sigma_alpha ^2), (22.33)
where the second equlaity assume cor [epsilon_it, y_i,t-1] = 0 and the third
equality is obtained after some algerbra for the special case of randome
effects with epsilon_ii iid [ 0, sigma_epsilon ^2] and alpha_i iid [0,
sigma_alpha ^2]
------------------------
In the next page they say that when gamma = 0. Cor (y_it, yi, t-1)
simplifies to
sigma_alpha^2 / (sigma_alpha ^2 _ sigma_epsilon ^2)
The last line suggests that may be extra parentheses are needed in the
denominator of 22.33.
I thought that I understood this material, but I am frutstated that I cannot
derive 22.33. It doesn't seem all that complicated, but my inability to
derive it makes me suspect that I did not understand this material as well
as I should.
I will appreciate it if you could help me.
Best regards,
Victor Waters
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**References**:**st: Not Directly Stata Related, But Please Help***From:*"Victor Waters" <[email protected]>

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