[Rd] mcnemar.test helpfile (PR#9220)

From: <candrews_at_buffalo.edu>
Date: Tue 12 Sep 2006 - 14:17:33 GMT


Full_Name: Chris Andrews
Version: 2.3.1
OS: Windows
Submission from: (NULL) (128.205.253.147)

?mcnemar.test

ends with an example:

     ## Agresti (1990), p. 350.
     ## Presidential Approval Ratings.
     ##  Approval of the President's performance in office in two surveys,
     ##  one month apart, for a random sample of 1600 voting-age Americans.
     Performance <-
     matrix(c(794, 86, 150, 570),
            nr = 2,
            dimnames = list("1st Survey" = c("Approve", "Disapprove"),
                            "2nd Survey" = c("Approve", "Disapprove")))
     Performance
     mcnemar.test(Performance)

## => very strong association between the two successive ratings

The example runs fine. The final statement ("very strong association between the two successive ratings") is true. But they are unrelated. McNemar's test is a test of marginal homogeneity. The conclusion should be that opinion has changed. The marginal distributions are different. The approval rating has dropped from 59% to 55% (p=4e-5).



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