On Mon, 30 Dec 2002 23:47:34 +0800, "K�J" <[EMAIL PROTECTED]> wrote:
> I hear people saying that t-tests could be used to test: > > 1. difference between two proportions You can use a t-test to test a 0/1 variable (proportions). Use the usual test, with the pooled variance estimate, if you are in the midst of reporting dozens of other results using a t. If you are trying to report a single result, folks will be happier if you give them the usual 2x2 contingency table, and the chi square value. > 2. difference between two mean differences (i.e. between (M12 - M11) > and (M22 - M21). If that is change-score(1) and change-score(2), where you can actually compute the scores, then you could make that the explicit case of comparing two scores: and that is where you would use a t-test automatically, based on the degrees of freedom for sample (1) + (2). In the more general ANOVA context, that might be a "special contrast". It can be reported as t, using the DF of the error term. Some folks prefer to report tests on contrasts as F-tests -- Once-upon-a-time, I ran into an innumerate reviewer who had a textbook with an example, and therefore wanted to insist that only F was acceptable. > Could somebody please advice me on this or give me a reference to read > about these tests? I think this went unanswered when posted in sci.stat.consult because the <above> are two Unusual Cases, and you give no hint about whether you recognize that... or just why it is that you are interested in testing in general, or t-tests in specific; or where you have looked already. For information, or for references: You could browse my stats-FAQ; also, the home pages of other people who post answers to these stats groups. -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
