< snip >
: Problem: In Principal Component Analysis (Varimax-rotation) both
: programs produce seven factors and all loadings are identical
: regarding their power. But, one factor produced by Systat has inverse
: loadings compared to what SPSS produces:
: Systat SPSS
: .787 -.787
: -.701 .701
: .666 -.666
: This is a real problem because we use factor scores based on these
"This is a real problem"? -- the serious problem is that you
believe that the DIRECTION of the scoring in Factor Analysis
has some meaning. But: it is 100% permissable to change the
signs on all the loadings of a factor. So, do it. See, the results
are the SAME!
If the algorithm does not leave coefficients that are mostly "+",
then some computer programs count the pluses and will reverse signs,
to make the NUMBER of loadings to be mostly positive; or get a sum
in order to make the TOTAL positive ... or, whatever.
It does not matter, mathematically, statistically, or clinically.
It is nice, in a way, that this problem comes up occasionally, because
there is a particular misunderstanding of Factors, arising from a
clinical rather than a mathematical perspective, which the explanation
should help to illuminate. But I forget how to describe it.
If this is still a problem for someone, please ask.
http://www.pitt.edu/~wpilib/index.html Univ. of Pittsburgh