Date: Tue, 3 Apr 2007 15:06:17 -0500
Reply-To: "Swank, Paul R" <Paul.R.Swank@uth.tmc.edu>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: "Swank, Paul R" <Paul.R.Swank@uth.tmc.edu>
Subject: Re: McNemar test
In-Reply-To: <C7C279D983E9C4488C3BFDB43C2DAE2C176606B7@ITEVS.uchc.net>
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I agree that McNemar's test is like a paired (or dependent samples) t
test but it works on a 2 by 2 table where the table represents paired
frequencies. For example, if 100 people report whether or not they agree
or disagree with two political statements, then the results can be
reported as a 2 by 2 table:
1st statement 2nd statement
agree disagree total
agree 30 10 40
disagree 20 40 60
total 50 50 100
The typical chi-squared test for such a table is a measure of
association between the statements Indicatig a significant relation
(chi-square(df=1, n=100) = 16.67; p < .01). The McNemar test is
concerned with the equality of the marginal proportions (p(1.) = P(.1).
That is, is the proportion who agree with the first statement (40%)
different from the proportion who agree with the second statement (50%)?
This is equivalent to the test of symmetry for the table (p(12) = p(21)
The large sample test statistic is chi-square(1) = (10 - 20)**2 /
(10+20) = 3.33; p > .05.
Paul R. Swank, Ph.D. Professor
Director of Reseach
Children's Learning Institute
University of Texas Health Science Center-Houston
-----Original Message-----
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of
Burleson,Joseph A.
Sent: Monday, April 02, 2007 12:27 PM
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: Re: McNemar test
Lou:
The McNemar test does not test the difference between the two
proportions in a 2 X 2 chi-square. It is used to assess change across
time (or some other within-subjects variable): does the change from 0 to
1 differ significantly from the change from 1 to 0, for example (it
ignores the frequencies of subjects who go from 0 to 0 and from 1 to 1).
Hence, it is like a "paired t-test" for dichotomous data.
See Siegel, S. (1956). Non parametric statistics for the behavioral
sciences. New York: McGraw-Hill. p. 63-67.
Joe Burleson
-----Original Message-----
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of
Lou
Sent: Monday, April 02, 2007 11:18 AM
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: McNemar test
Dear all,
Could someone please advise on the best way to report the results of a
McNemar test. If I state beforehand that I am using McNemar, do I
simply label the test statistic as being 'chi-square'?
For example, I have compared the proportions 82.59% and 76.62%. This
gives a value of the McNemar statistic of 172.567 with p < 0.001 and N =
7920. I have calculated a 95% confidence interval for the difference of
(5.09%, 6.85%).
I would like to report this (and similar) information in the most
accurate and way possible. Suggestions please?
Many thanks,
Lou
