Thanks Mike - that's very helpful. In the meantime, I have found that, for
large n, there is a fairly straghtforward linear relationship between n
(sample size) and the inverse chi square at any given probablity (and inverse
chi square at 50% comes out to be n+1 or v+2 where v is degrees of freedom).
However, probably best to actually calculate the chi square velaues I need so
I will definately try the function and have a look at the notes.
Many thanks and best wishes, Boris.

"Mike Middleton" wrote:

Boris -

Is there a workaround? <

One possible workaround is to use Ian Smith's inv_chi_sq function, one of
his many VBA statistical functions.

His file can be downloaded from
http://members.aol.com/iandjmsmith/Examples.xls

And David Heiser has some notes at
http://www.daheiser.info/excel/notes/notead.pdf

- Mike
www.MikeMiddleton.com


"Boris" wrote in message
...
Hi,
I am having some real problems with the CHIINV function in Excel (I am
using
Excel 2007 but the same seems to be true of all previous versions of
Excel -
at least back to 2002 - too). According to the help file, CHIINV can take
probabilities = 0 and <= 1 (just as well that it can - though there seems
to
be an issue with the 50% probability) and degrees of freedom up to but not
including 10^10 (ie 10 billion). However, when you try to calculate a
chiinv
of, say 0.05 probability, and you set the degrees of freedom to anything
above 1806, the formula immediately returns #NUM! Now, 1806 is much much
smaller than 10^10 so should be perfectly legitimate. In my application in
need to generate chiinv for degrees of freedom up to 90000 (still much
less
than the 10^10 given in the function reference) and so I am really getting
stuck...
Is this a bug? Is there a workaround? Anyone have any suggestions for what
may be limiting the chiinv degrees of freedom to <=1806 and why this
particular number should be the limiting value?
I would really appreciate any hints (and confirmation that this error is
persistent across platforms and versions of Excel as I have only been able
to
try it on a few machines running Excel XP, 2003 or 2007). If anyone knows
of
a clever way to work around this apparent problem, that would be extremely
interesting...
Many thanks and best wishes, Boris.