How to determine if a number is statistically meaningful

From: davegb (davegb_at_safebrowse.com)
Date: 03/21/05 

Date: 21 Mar 2005 14:00:16 -0800

I've posted another thread about this situation, but I have a separate
question concerning the same dataset.
I have statistical info about state clients for the 64 counties in the
state. I have the total number of clients over a year, and the number
of clients who'd had a specific occurence during that time. The
statewide average for this occurence is about 4%. Of course, I have
some small, rural counties with only a few clients (and a few with
none, which doesn't matter). If 1 of 4 clients experiences the
occurence, it's statistically misleading to report on the spread***
that the county had a 25% occurence rate. I'd like to suppress those
numbers when they would be misleading.
How do I determine the threshold at which the numbers become
statistically relevant? Or the inverse, irrelevant?
Any help here would be greatly appreciated. I'm not a statistician, but
have an engineering degree and still remember a little statistics, but
not much! But at least I can figure out the math, and use the functions
in Excel to make all this happen.