"polychoric estimates polychoric and polyserial correlations, and
polychoricpca performs the principal component analysis on the resulting
correlation matrix. The current version (1.4) of the routine requires Stata 8.2.
"The polychoric correlation of two ordinal variables is derived as follows.
Suppose each of the ordinal variables was obtained by categorizing a
normally distributed underlying variable, and those two unobserved variables
follow a bivariate normal distribution. Then the (maximum likelihood)
estimate of that correlation is the polychoric correlation. If each
of the ordinal variables has only two categories, then the correlation
between the two variables is referred to as tetrachoric."
Hope this helps.
--Mark
Quoting Patricia Sourdin <[email protected]>:
> Hi Statalist
> just a query on -factor-.
> I am trying to construct an index where I have five variables which
> are binary
> indicators.
> I have read somewhere that it is not appropriate to use factor
> analysis if the
> variables are binary. Can anyone confirm, please?
> Also, would -pca- be an alternative in this case?
> As usual, any help would be appreciated.
> Patricia
> *
> * For searches and help try:
> * http://www.stata.com/support/faqs/res/findit.html
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
>
Prof. Mark Schaffer
Director, CERT
Department of Economics
School of Management & Languages
Heriot-Watt University, Edinburgh EH14 4AS
tel +44-131-451-3494 / fax +44-131-451-3008
email: [email protected]
web: http://www.sml.hw.ac.uk/ecomes
________________________________________________________________
DISCLAIMER:
This e-mail and any files transmitted with it are confidential
and intended solely for the use of the individual or entity to
whom it is addressed. If you are not the intended recipient
you are prohibited from using any of the information contained
in this e-mail. In such a case, please destroy all copies in
your possession and notify the sender by reply e-mail. Heriot
Watt University does not accept liability or responsibility
for changes made to this e-mail after it was sent, or for
viruses transmitted through this e-mail. Opinions, comments,
conclusions and other information in this e-mail that do not
relate to the official business of Heriot Watt University are
not endorsed by it.
________________________________________________________________
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
