The lack of independence between some subjects will invalidate the assumption of independence for the model. This would have likely impact on the significance tests.
Dr. Paul R. Swank,
Professor and Director of Research
Children's Learning Institute
University of Texas Health Science Center-Houston
-----Original Message-----
From: SPSSX(r) Discussion [mailto:
[hidden email]] On Behalf Of Murni Po
Sent: Wednesday, June 10, 2009 2:37 AM
To:
[hidden email]
Subject: t-test
Hi,
I have just been reading a longtudinal study which measured people attitude
toward recycling at 4 different times. At each time of measurement, they
have repeated participants and new participants. Then the researchers used
independent t-test to see whether people attitude changes at different time
(e.g. time 1 and 2). Is this statistically correct? To me, independent
t-tests assumes all participants are different in time 1 and 2. There were
about 300 participants and about 60 participants participated in all study.
If you could shed some light why this would statistically okay or
potentially disaster, that will be very helpful to me.
Thanking you for your time in advance.
murni
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