I think all the comments supplied by other posters are relevant.
Of course you should check to make sure that SAS is reading the input
matrix correctly, as was pointed out. However, even assuming that you
did everything correctly I'm not surprised that SAS has a problem
factoring the matrix. A correlation matrix composed of tetrachorics
may not be factorable--especially if there is a large number of items.
That can be remedied by "conditioning" the matrix. For a discussion,
see the paper by Knol and Berger (the Parry & McArdle paper might also
talk about this):
Knol DL, Berger MP. Empirical comparison between factor analysis and
multidimensional item response models. Multivariate Behavioral
Research, 1991, 46, 457-477.
Parry CD, McArdle JJ. An applied comparison of methods for least-
squares factor analysis of dichotomous variables. Applied Psychological
Measurement, 1991, 15, 35-46.
Note that conditioning the matrix in this way is a completely "ad hoc"
procedure.
Hope this helps.
--
John Uebersax
[EMAIL PROTECTED]
Sent via Deja.com http://www.deja.com/
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