Date:         Mon, 3 Jul 2006 14:07:20 +0200
Reply-To:     Marta García-Granero
              <biostatistics@terra.es>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Marta García-Granero
              <biostatistics@terra.es>
Organization: Asesoría Bioestadística
Subject:      Re: Help with Cochran Test please? CORRECTED VERSION!
In-Reply-To:  <200607031049.k63AkU5E008477@mailgw.cc.uga.edu>
Content-Type: text/plain; charset=ISO-8859-1

Hi Lou,

I *think* that the first value encountered is treated as a success.
See the difference for this dataset:

DATA LIST FREE /march june august (3 F8.0).
BEGIN DATA
0 1 0 0 0 0 0 1 0 1 0 0 1 1 0 1 0 0
0 0 0 1 1 0 1 1 0 1 0 0 1 0 0 1 1 0
0 1 1 0 1 1 0 0 0 0 1 0 0 1 0 1 0 0
1 0 0 1 0 0 1 0 1 1 1 1 1 0 0 1 1 0
END DATA.
VALUE LABEL march TO august 0'Negative' 1'Positive'.
LIST.

NPAR TESTS /COCHRAN = march june august.

SORT CASES BY march(D).
NPAR TESTS /COCHRAN = march june august.

L> The results gave the following:
L> N = 7274
L> Cochran’s Q = 79.121*
L> df = 2
L> Asymp. Sig = 0.0001
L> * 0 is treated as a success.

L> I assume I have done everything right here from what I understand.  My
L> only question/query is that sometimes the test treats ‘1’ as success and
L> sometimes it treats ‘0’ as success.  Is there a way to always ensure
L> that ‘1’ is treated as success?  Why does the test do this in SPSS?  How
L> does this affect my interpretation of the results?

It doesn't affect at all.

BTW, do you want to run post-hoc comparisons (compare "rd" pairwise)?

Other topic: you mentioned that you wanted to test whether there were
differences in trend among age groups. These could be done (with a bit
of manual work or writing some matrix code) adapting the heterogeneity
test described by Sokal & Rohlf in their book "Biometry". Try to take
a look at it (I can't fotocopy pages of mine, because it is in
Spanish). I'm off soon until the 17 of july (I always abandon my city
when San Fermines, the "Running of the Bulls", because I can't stand
the sight of hundreds of drunkards sleeping in the middle of our
beautiful city gardens, treading the flowers, and I don't enjoy going
to the arena either to watch a splendid animal die either...). If you
can wait until I'm back, then I could write some syntax for that task.

Regards

Marta