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Re: st: Peer variable coefficient estimate nonsense

 From Jian Zhang To statalist@hsphsun2.harvard.edu Subject Re: st: Peer variable coefficient estimate nonsense Date Sat, 3 Mar 2012 12:26:10 +0800

```Hi Clyde Schechter,

thanks for your comments. as you guessed, the peer group is the
student's class and the score is his/her math score.  In my regression
analysis I include grade and time semester dummies, i.e., I have
controlled for grade and semesters.  Thus this means what i am looking
at is students who are in the same semester and grade: I am comparing
students in the same grade and same semester.  Then the question is
really: given a student, 1 year older of his peers matters more than 1
year older of his own age to his math achievement? For such a student,
it seems that his own age matters more than his peer average ages to
math achievement. Of course, there is no theory/empirical evidence
supporting this.  it is just out of my bold intuition...

Jian

On Sat, Mar 3, 2012 at 1:52 AM, Clyde B Schechter
<clyde.schechter@einstein.yu.edu> wrote:
> Leaving aside the technical issues brought up by Nick Cox of how correlated variables might partition variance among themselves in a regression analysis, substantively, I wonder why Jian Zhang thinks it is nonsensical for peer age to be a stronger predictor of student score than the student's own age.  It isn't explained what kind of scores and peer groups these are, but if the "peer" group in question is the student's class, it wouldn't surprise me at all that mean peer group age, which is then a very strong proxy for grade level, would be a stronger predictor of, say, math achievement, than the child's individual age when the two are used together.  In fact, it _would_ surprise me if the opposite were true.  After all, we would expect 5th graders to have higher math scores than 4th graders, but there is no reason to think that an older 4th grader would outperform a younger 5th grader.
>
> More generally, there are many other instances where a group attribute is a stronger predictor of an individual outcome than the analogous attribute of the individual.
>
> Clyde Schechter
> Dept. of Family & Social Medicine
> Albert Einstein College of Medicine
> Bronx, NY, USA
>
>
>
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