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Re: st: RE: Measures of association for a small sample


From   Robert A Yaffee <bob.yaffee@nyu.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: Measures of association for a small sample
Date   Wed, 11 Jan 2012 00:03:53 -0500

Francisco,
   You are skating on thin statistical ice.  But with such a small sample size
you have what Damodar Gujarati calls the problem of micro-numerosity,
which his what others call finite samples, which are
not in general conformity with the laws of large numbers.  This is
territory where asymptotics are not going to be of much help
in attaining a population estimate.  You might want to do a power
analysis to get an idea of your probability of failing to detect
a significance of a medium effect size.

   You could consider bootstrapping or permutation tests if you were
sure that your data were representative.
         Regards,
             Robert

On Tue, Jan 10, 2012 at 10:31 AM, Lachenbruch, Peter
<Peter.Lachenbruch@oregonstate.edu> wrote:
> If you have the entire population, why do you need significance tests?  Isn't the measure sufficient?
>
> ________________________________________
> From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of Francisco Rowe [frowe@ucn.cl]
> Sent: Tuesday, January 10, 2012 4:35 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: Measures of association for a small sample
>
> Hi,
>
> Sorry for taking advantage of statalist for this -I am trying to measure the association between two variables with a reduced number of observations (13) which constitutes my entire population.
>
> I have utilised pairwise correlation coefficients (pwcorr) and regression using an Iteratively Reweighted Least Squares (IRLS) estimation (rreg) (on cross-sectional data). However, given some of the assumptions of these measures, the results can be questioned. For this reason, I would like to implement some additional tests or measures on my data.
>
> Would it be possible to have some guidance on this?
> Are regressions based on IRLS useful in this context?
> Which non-parametric measure can it be useful?
>
> Thanks in advance.
>
> Francisco.
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-- 
Robert A. Yaffee, Ph.D.
Research Professor
Silver School of Social Work
New York University

Biosketch: http://homepages.nyu.edu/~ray1/Biosketch2009.pdf

CV:  http://homepages.nyu.edu/~ray1/vita.pdf

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