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Re: st: basis for selection of observations for nonparametric correlation?
From
Nick Cox <[email protected]>
To
[email protected]
Subject
Re: st: basis for selection of observations for nonparametric correlation?
Date
Mon, 4 Jul 2011 08:47:30 +0100
Stata ignores observations in which _any_ value is missing. Zeros are
values like any other so far as Spearman correlation is concerned; in
any case they are ranked before the correlation is calculated, so the
fact that any values are zeros is hidden as well as immaterial.
Nick
On Mon, Jul 4, 2011 at 8:19 AM, Edith Marshall <[email protected]> wrote:
> 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.
>
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