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# Re: st: Comparing Regression Coefficients Across Subsamples

 From Nick Cox To statalist@hsphsun2.harvard.edu Subject Re: st: Comparing Regression Coefficients Across Subsamples Date Mon, 6 Aug 2012 12:59:29 +0100

```Several questions are bundled together here. Working backwards from
the easiest:

3. Analysis of variance is the method centred on the comparison of
means of several groups.

2. However, your dataset is a panel dataset gathered over time and so
plain analysis of variance is unlkely to be suitable. Much depends on
quite what dependence structure you think underlies your data and thus
your regressions (of what on what?).

1. I can't comment on Cohen's recipes as I have not read the paper cited here.

Nick

On Mon, Aug 6, 2012 at 12:07 PM, David Ashcraft
<ashcraftd@rocketmail.com> wrote:

> I am working on a panel data of more than 200 firms with distinct "id" over 20 years with monthly frequency. Each firm belongs to one of the three groups (1,2 and 3) based on regional affiliation. Exit and entry is unrestricted. The resulting data set in unbalanced. I Now I want to compare the regression coefficients of each regional group in the light of discussion provided in:
>
>
> Cohen,
> A. (1983). Comparing Regression Coefficients Across Subsamples A Study of
> the Statistical Test. Sociological Methods & Research,vol. 12(1) pp 77-94.
> doi: 10.1177/0049124183012001003
>
>
> I believe -ttest- i.e. differences in means analysis over coefficients of each group is what Cohen A . (1983) is referring to. Am I right about this? Please tell me, if there is any other command that can be used to implement Cohen A. (1983)
>
> Aside from that _ttest- compare means between two groups at a time. In my case what should I do to test for three groups at the same time?

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