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# Re: st: Re:

 From David Ashcraft To "statalist@hsphsun2.harvard.edu" Subject Re: st: Re: Date Wed, 30 Nov 2011 19:04:09 -0800 (PST)

```Steve,

Can you please explain a little further. Let me rephrase the question initially asked. Whether coefficients obtained after running regression on all managers (full dataset) are same as the average coefficients obtained from running regressions on individual mangers. I don't know a paper that has done analysis on this pattern, and would like to know, if there exist any analysis like that. My idea is, both method should reflect the similar results.

David

----- Original Message -----
From: Steve Samuels <sjsamuels@gmail.com>
To: statalist@hsphsun2.harvard.edu
Cc:
Sent: Thursday, December 1, 2011 1:39:29 AM
Subject: Re: st: Re:

Yuval,

I don't have access to your article, but I have an observation: The predictions (real and counterfactual) that are averaged are not independent, because they are all functions of the estimated regression coefficients. I don't think a t-test accommodate the non-independence. In Stata, I would use -margins- or -lincom- after -margins-.

Steve

On Nov 26, 2011, at 9:09 AM, Yuval Arbel wrote:

David,

You can simply use Difference in Difference (DD) analysis:

Run a regression on the group of managers who take the first (second)
approach. Then predict what would have happened to the performance of
each manager in the case that he/she takes the other approach and use
the -ttest- to see whether the difference is significant.

Note to define dummy variables in any case that variables are ordinal,
i.e., the numerical values have no quantitative meaning

I use this approach quite often. You can look at the second part of my
following paper published in RSUE:

Arbel, Yuval; Ben Shahar,Danny; Gabriel, Stuart  and Yossef Tobol:
"The Local Cost of Terror: Effects of the Second Palestinian Intifada
on Jerusalem House Prices".Regional Science and Urban Economics (2010)
40:  415-426

On Sat, Nov 26, 2011 at 12:11 PM, David Ashcraft
<ashcraftd@rocketmail.com> wrote:
> Hi Statalist,
>
> This is more like an econometric than a Stata question. I am little lost on the following scenario:
>
> The situation is: I want to measure the performance of managers, who has a specific approach against those who do not. I have several individual managers in each category. One way is to regress the performance of these managers against their benchmark for the whole data using
> -regress manager benchmark, by(belief)
> The second option is to run individual regression on each manager and get the coefficients of individual regressions and run a ttest alpha, by(belief) .
>
>
> Now the question is, how different is the result from the ttest of alpha from that of the alpha of the regression equation.
> Any help will be really appreciated.
>
> If anyone can suggest an academic paper on similar scenarios, that would be a great help.
>
>
> David
>
> *
> *   For searches and help try:
> *  http://www.stata.com/help.cgi?search
> *  http://www.stata.com/support/statalist/faq
> *  http://www.ats.ucla.edu/stat/stata/
>

--
Dr. Yuval Arbel
4 Shaar Palmer Street, Haifa, Israel
e-mail: yuval.arbel@gmail.com

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```

• References:
• [no subject]
• From: David Ashcraft <ashcraftd@rocketmail.com>
• st: Re:
• From: Yuval Arbel <yuval.arbel@gmail.com>
• Re: st: Re:
• From: Steve Samuels <sjsamuels@gmail.com>