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Date:         Mon, 29 Oct 2001 10:45:01 +0100
Reply-To:     Gijs Dekkers <gd@PLAN.BE>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Gijs Dekkers <gd@PLAN.BE>
Organization: planbureau / bureau de plan
Subject:      Re: question on FACTOR
Content-Type: text/plain; charset=us-ascii

Dear David,

This is the source code:

proc factor data=datin method=principal scree mineigen=0 priors=asmc rotate=varimax nfactors=4 corr outstat=factout out=datuitF ; var spreken sarm cowoko garbeid is_wcomfort ziekte is_opl1 is_tevr is_socint1 is_socint2 is_socint3 ; run ;

As you can see, there is nothing special about it. But the results are stunning.

1. In the case of an orthogonal rotation, some of the factors all of a sudden are correlated. 2. In the case of an oblique rotation, it sometimes happens that the "inter-factor correlations" are not equal (even of the opposite sign) from semipartial correlations which I derived afterwards, using PROC CORR.

I serially omit all variables (i.e. I let them out of the analysis one after another) to find out if it was just one variable which caused this, but no. It is a complete mistery to me. Any help would be greatly appreciated.

Gijs

"David L. Cassell" wrote:

> Gijs Dekkers replied [in part]: > > That, unfortunately, is not the issue. I agree with you on the scree, > but my problem > > arises way after the number of factors have been chosen. It is very > simple: I choose 3 > > factors and did not rotate the solution. I then used PROC CORR to find > 3 factors that > > are uncorrelated. > > > > Next, I run the same program, but this time, I rotated orthogonally. > And, all of a > > sudden, my factors (_not_ pseudo-factor scores) were highly > correlated. And that's > > when I was completely flabbergasted... > > I would be too. PROC FACTOR by default will generate uncorrelated > factors. But not > all rotations are created equally. Which rotation did you use? Many > optimize other > features of the data by making a non-orthogonal rotation of the data, > after which the > new factors would indeed be correlated. > > David > -- > David Cassell, CSC > Cassell.David@epa.gov > Senior computing specialist > mathematical statistician

-- dr. Gijs Dekkers Federaal Planbureau Algemene Directie Kunstlaan 47-49 B 1000 Brussel ++32/(0)2/5077413 fax 7373


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