Re: st:AR(1) error notice: sample may not include multiple panels

[Richard Herron <richard.c.herron@gmail.com>]

This question came up yesterday, too. Here was my response:

Panels require strict exogeneity for consistency, so you can't have
lagged dependent variables on the right hand side (i.e., dynamic
panels aren't allowed).

If you think about the within estimator for panel data, then you have
y_{i, t-1} - mean(y_i) on the right hand side, which is not orthogonal
to e_{i,t} because mean(y_i) contains y_{i,t} from the left hand side.

There are some solutions to this in -xtabond-, which does the Arellano
and Bond estimator. Arellano and Bond correct the endogeneity by
estimating the dynamic panel in first differences and using lags as
instruments and GMM to take care of over-identification.

Chapter 9 in Cameron and Trivedi's "Microeconometrics Using Stata"
provides a handful of techniques for estimating dynamic panel models.
Chapters 21 and 22 in their Microeconometrics textbook provides more
theory. HTH.

On Sat, Mar 17, 2012 at 18:02, Amanda Fu <mandy.fu1@gmail.com> wrote:
> Dear Statalists,
>
> Sorry for bothering you with  a question about a simple AR(1)
> estimation. I searched related discussion in the archives , but still
> cannot figure out why the error message comes out. Any suggestions
> will be helpful.
>
> I want to estimate a univarate AR(1) model (without any controls). The
> data set is a panel data,  including 1000 observations for 5 years
> (200 variables. The one I am interested is enroll taking values 0,1) .
> . tsset id years
> . arima enrollment,ar(1)
> "sample may not include multiple panels"
>
> I must have missed something here. Can someone give me some hints?
> In addition, instead of using ARIMA, may I know if there is any easy
> alternative to do the AR(1) ?
>
> Thank you very much!
>
> Amanda
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