From: Jonathan Baron <baron_at_psych.upenn.edu>

Date: Mon 18 Jul 2005 - 05:05:52 EST

Date: Mon 18 Jul 2005 - 05:05:52 EST

On 07/17/05 20:12, Rafael Laboissiere wrote:

> Thanks for your reply, Jonathan. Thanks also to Spencer, who suggested

*> using the BTm function. I realize that my description of both the
**> experiment and the involved issue was not clear. Let me try again:
**>
**> My subjects do a recognition task where I present stimuli belonging to
**> three different classes (let us say A, B, and C). There are many of
**> them. Subjects are asked to recognize each stimulus as belonging to one
**> of the three classes (forced-choice design). This is done under two
**> different conditions (say conditions 1 and 2). I end up with matrices of
**> counts like this (in R notation):
**>
**> # under condition 1
**> c1 <- t (matrix (c (c1AA, c1AB, c1AC,
**> c1BA, c1BB, c1BC,
**> c1CA, c1CB, c1CC), nc = 3))
**> # under condition 2
**> c2 <- t (matrix (c (c2AA, c2AB, c2AC,
**> c2BA, c2BB, c2BC,
**> c2CA, c2CB, c2CC), nc = 3))
**>
**> where "cijk" is the number of times the subject gave answer k when
**> presented with a stimulus of class j, under condition i.
**>
**> The issue is to test whether subjects perform better (in the sense of a
**> higher recognition score) in condition 1 compared with condition 2. My
**> first idea was to test the global recognition rate, which could be
**> computed as:
**>
**> # under condition 1
**> r1 <- sum (diag (c1)) / sum (c1)
**> # under condition 2
**> r2 <- sum (diag (c2)) / sum (c2)
**>
**> The null hypothesis is that r1 is not different from r2. I guess that I
**> could test it with the chisq.test function, like this:
**>
**> p1 <- sum (diag (c1))
**> q1 <- sum (c1) - p1
**> p2 <- sum (diag (c2))
**> q2 <- sum (c2) - p2
**> chisq.test (matrix (c(p1, q1, p2, q2), nc = 2))
**>
**> What do you think?
**>
**> I also thought about testing the triples like [c1AA, c1AB, c1AC] against
**> [c2AA, c2AB, c2AC], hence my original question.
*

-- Jonathan Baron, Professor of Psychology, University of Pennsylvania Home page: http://www.sas.upenn.edu/~baron ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.htmlReceived on Mon Jul 18 05:13:30 2005

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