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From: Richard MacLennan
Subject: Correlation
Date: Fri, 24 Oct 2008 14:14:09 -0600


    I read some of your online blogs, but I could not find a simple way
to contribute to the discussion, so I thought I would do so through
email. I am using version 0.4.0, whcih is what you seem to be
distributing with PSPPIRE. My apoligies if you have fixed the following
bugs in later versions.

1. Someone requested correlations. Someone else recommend using the
correlation option in the CROSSTAB procedure in the Descriptives menu. I
would advise against this. The default correlations it reports (phi &
Cramer's V) are only relevant for 2 x 2 and larger contingency tables,
respectively. This would not be suitable for the most common
applications of correlation.

2. To obtain correlations, instead I would recommend using the PAIRED
TTEST procedure in the Compare Means menu. The correlation reported here
is the equivalent of a PEARSON CORR between the two paired variables.

3. BTW, I would not trust the significance test for the t-test value in
the PAIRED procedure. I tested in with the Employee.sav file from SPSS,
and it reports p = 2.000. I hope that even non-statisticians would
realize this value is incorrect.

4. In your documentation you do not really clarify whether PEARSON CORR
is an implemented or non-implemented procedure. It appears to be
non-implemented. However, it would not seem hard to do so, since you
already have it coded for the PAIRED TTEST procedure (although of course
you do not have the complete syntax for PEARSON CORR coded).

I hope this info helps you endeavours to develop an SPSS clone.

Good Luck!

Richard MacLennan

Richard MacLennan, Ph.D.
Professor, Psychology 
Room 343 Ad. Hum. Bldg.
University of Regina
REGINA, Saskatchewan
S4S 0A2  Canada
Tel.: (306) 585-4458
Fax: (306) 585-5429 

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