home *** CD-ROM | disk | FTP | other *** search
- Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU
- Path: sparky!uunet!utcsri!newsflash.concordia.ca!garrot.DMI.USherb.CA!uxa.ecn.bgu.edu!psuvax1!psuvm!auvm!BLEKUL21.BITNET!LAAAA02
- Organization: K.U.Leuven (Belgium)
- Message-ID: <STAT-L%92111710030539@VM1.MCGILL.CA>
- Newsgroups: bit.listserv.stat-l
- Date: Tue, 17 Nov 1992 11:14:10 UTC+0100
- Sender: "STATISTICAL CONSULTING" <STAT-L@MCGILL1.BITNET>
- From: Vuylsteke Magda <LAAAA02@BLEKUL21.BITNET>
- Subject: Re: factor analysis
- Lines: 59
-
- > About April Milliken's question:
- >
- > I agree with Andy Taylor that this looks more like a MANOVA question.
- > There are some problems with MANOVA. It assumes equal covariance matrixes
- > over time points. Also, it gives you in fact a kind of factor analysis,
- > because it gives you that linear combination of dependent variables that
- > produces the largest separation between the groups. This linear combination
- > may or may not be interpretable in view of the substantive problem.
- > If you use factor analysis, you are in fact assuming that the factor structure
- > across time points is the same (this assumption is a bit less restrictive than
- > the equal covariance matrices in manova). There are Lisrel models for panel
- > data that would apply, but I think your canine sample is to small to use Lisre
- > A reason to use factor (preferably component-) analysis in stead of manova
- > would be that the factors might be more interpretable than what manova gives
- > you. If you want to use factor analysis, I would recommend a procedure like
- > this:
- > 1) if the dependent variables are reasonably normal, use manova or discriminan
- > (in SPSS) to test for equality of coveriance matrixes across time points. If
- > variables have non-normal distributions, don't bother because the Box test
- > used for this is extremely sensitive to non-normality.
- > 2) split your variables in group means (aggregate in spss) and individual
- > deviations from the group means (groups defined by different time points).
- > 3) the correlations of the individual deviation scores will reflect all that
- > is similar within the groups; do a component analysis on these.
- > 4) the correlations of the group means reflect variation between groups; do a
- > component analysis on these too.
- > 5) If the results from 4) look very different than the results from 3),
- > the assumption of similar factor structures at the different time points
- > is violated. This means trouble. Strew ash on your hair, go home and mourn.
- > 6) If 4) looks reasonably similar to 3), use the results from the within
- > groups analysis in 3). If you can interpret them (f.i., can you interpret
- > some factor as canine well-being), derive a formula to compute factor scores,
- > compute these at all different time poins in the same way (using original
- > variables) and do univariate anovas on these (manove is not really needed
- > because your factor scores will be nearly orthogonal).
- > 7) Some statisticians may feel that this analysis is a bit messy. I agree it
- > is, but it may give you more insights than doing a manova straightaway.
- > 8) A useful reference is: K. Harnkvist (1978). In Journal of Educational
- > Psychology, 70, 706-16. A more modern approach is an article by B.O. Muthen
- > in Psychometrika, 1989, 54: 557-85. But Muthen uses a latent variable approac
- > assuming large samples.
- >
- > Hope this sparkles some discussion
- >
- > Joop Hox
- > University of Amsterdam
-
- Is this not about the same as doing a CANONICAL DISCRIMINANT ANALYSIS
- or perhaps is it better to do a CANONICAL CORRELATION ANALYSIS with
- dummy variables for groups as one set of variables. Some computer
- programs give more output for the last analysis.
-
- Drs. Magda Vuylsteke Telephone (32)-16-286611 ext2215
- Computing Center Fax (32)-16-207168
- Center of Statistics
- University of Leuven
- de Croylaan, 52a
- 3001 Heverlee E-mail:laaaa02@blekul21
- Belgium
-