Factor Analysis in MASS4

Dear Kevin,

I had a look at the MASS4 scripts in the MASS package, in Ch 11.3 Factor
Analysis, there is a section of codes like:

  data(ability.cov)

  ability.FA <- factanal(covmat = ability.cov, factors = 1)
  ability.FA
  (ability.FA <- update(ability.FA, factors = 2))
  #summary(ability.FA)
  round(loadings(ability.FA) %*% t(loadings(ability.FA)) +
             diag(ability.FA$uniq), 3)

Unfortunately I still haven't received the book I ordered, so I can't look
this up.

I, too (and I'm sure many others) are also waiting.

Two questions:

1) What does the update() do?  I mean, what happens if I replace it with
     factanal(covmat = ability.cov, factors = 2)

As is generally the case, update methods allow you to respecify a model, 
here a factor analysis, changing some arguments to the modeling function. 
As you probably discovered, factanal(covmat = ability.cov, factors = 2) is 
equivalent.

2) What does the last command, the formulae in round() mean?  I tried it
and it produced a matrix that looks kind of like correlation matrix of
some sort...

These are the reproduced correlations, which may be compared with the 
observed correlations, round(ability.FA$correlation, 3).

I hope that this helps,
  John
-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox
-----------------------------------------------------

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._