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st: basis for selection of observations for nonparametric correlation?


From   Edith Marshall <edie.marshall@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: basis for selection of observations for nonparametric correlation?
Date   Mon, 4 Jul 2011 00:19:27 -0700

Hello, all

Please forgive my ignorance and, thus, need to post - I am new to
STATA and rusty with my stats!

I am running Spearman's rank correlation (nonparametric) on a data set
of 167 observations.  I have some missing values and legitimate zeros.
 After selecting the variables of interest and specifying that I want
to see the the correlation coefficient, the number of observations,
and the significance value, I get my correlation results table.  The
number of observations is 27 for all variable comparisons.  When I
check the box that forces all observations to be considered and re-run
the analysis, I get between 24 and 167 observations used for the
different comparisons.

Can anyone tell me the basis for which observations are used (the
default) when I don't force all of them in?  I need to decide which
correlation results to use and don't understand how STATA has selected
the 27 from the 167.  Obviously, I would prefer to have more
observations but also want the results to be legitimate.

Thanks in advance for all of your valuable input!!

Best,
E Marshall

--
Edie Marshall
DVM, MPVM, DACVPM

--
Edie Marshall
DVM, MPVM, DACVPM

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