Date: Thu, 11 Sep 2008 09:49:31 0400
ReplyTo: "Burleson,Joseph A." <burleson@up.uchc.edu>
Sender: "SPSSX(r) Discussion" <SPSSXL@LISTSERV.UGA.EDU>
From: "Burleson,Joseph A." <burleson@up.uchc.edu>
Subject: Re: paired vs independent samples ttest
InReplyTo: A<96845.10603.qm@web45103.mail.sp1.yahoo.com>
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No, the paired ttest will always be as or more significant. If the correlation between the pre and the posttest is exactly r = 0.000, then the two tests will be equal. If the r = 1.000, then the difference scores between the pre and the posttest will all be identical, meaning that the SD of the difference scores will be zero. In this case, all differences will be infinitely significant.
Joe Burleson
Original Message
From: SPSSX(r) Discussion [mailto:SPSSXL@LISTSERV.UGA.EDU] On Behalf Of Humphrey Paulie
Sent: Tuesday, September 09, 2008 3:34 PM
To: SPSSXL@LISTSERV.UGA.EDU
Subject: paired vs independent samples ttest
Dear all,
in pretest posttest studies where only one group in involved for comparing the means before and after treatment "paired samples ttest" is required. is that right?
i was just wondering how can independent samples ttest in such a situation change the results. I mean is it possible to find a mean difference significant with a pairde ttest and insinificant with an independent ttest?
cheers
Humphrey
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