st: Limits to df in invnchi2

[Marcello Pagano <Pagano@hsph.harvard.edu>]

Jeffrey Simons(jsimons@usd.edu) is having trouble posting this:

From Stata manual:

invnchi2(n,L,p) returns the inverse cumulative noncentral chi-squared
distribution.  If nchi2(n,L,x) = p, then invnchi2(n,L,p) = x (n must be 
an integer,1<=n<=200, 0<=L<=1000).

Why does n (the degrees of freedom) need to be <=200?

I am trying to utilize MacCallum et al., (1996) formulas for determining
sample size for covariance structural models. He provides equations and 
SAS code at the end of the article and it involves the above chi2 
distributions.

I wrote a program to do this in Stata but naturally, the model I want to
test has 246 degrees of freedom.  Why is there this limit?

Thank you
--
______________________________________________________________________

Marcello Pagano
Biostatistics Department               Tel: 1-617-432-4911
Harvard School of Public Health        Fax: 1-617-739-1781
655 Huntington Avenue                  email:pagano@biostat.harvard.edu
Boston, MA  02115                      http://biosun1.harvard.edu/~bio200
USA

eppur si muove


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