Angie,
My third message:
Besides conceptual issues addressed in my previous messages, I should call
your attention to the fact that 50 variables with 500 cases is very likely
to yield non-significant results, due to small size of sample in relation to
the number of variables.
Some books or teachers speak about an absolute minimum of 10 cases
per
variable. With 500/50 you are precisely at that supposed minimum, but it is
widely seen as too optimistic. 40-60 cases per variable is more like it,
although there is no general rule because all depends on the amount of
correlation among the observed variables.
Have you considered dividing the 50 items into a number of groups evidently
related to different dimensions? PCA performed on each group of more closely
related dichotomous variables may be more reliable, both because they are
more closely related and because the cases/variables ratio is higher.
Hector
-----Original Message-----
From: SPSSX(r) Discussion [mailto:
[hidden email]] On Behalf Of
Angelina S. MacKewn
Sent: 13 January 2010 19:41
To:
[hidden email]Subject: Factor Analysis on dichotomous variables
What is the factor analysis (PCA) equivalent that can be run on
dichotomous
variables. I have 50 exhibited behaviours (yes/no) that I want to factor
together. I have a sample size of about 500. I would be using SPSS and could
use syntax if it is available.
Thanks,
Angie
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