Chi Squared Distribution with Over 100 Degrees of Freedom

Date: 03/21/2005 at 07:23:13
From: Simon
Subject: chi squared distribution

I want to find the critical value for the chi squared distribution 
with 198 degrees of freedom.  I can only find tables on the internet 
up to 100 degrees of freedom.  Can you help?

Date: 03/21/2005 at 10:17:18
From: Doctor George
Subject: Re: chi squared distribution

Hi Simon,

Thanks for writing to Doctor Math.

The chi squared distribution is asymptotically normal as the number of
degrees of freedom (n) becomes infinite.  Since the chi squared
distribution has mean = n and variance = 2n, you can get a very good
approximation using the normal distribution with this mean and variance.

If you try this experiment with 100 degrees of freedom you will see 
that the approximation is very good.  That is why tables are usually
not made for more degrees of freedom.

If you do not think the approximation is good enough you will probably
need to write or buy software to do the calculations.

Does that make sense?  Write again if you need more help.

- Doctor George, The Math Forum
  http://mathforum.org/dr.math/