chi square but very disparate sample sizes

Posted by sgthomson99 on Oct 22, 2014; 6:28pm
URL: http://spssx-discussion.165.s1.nabble.com/chi-square-but-very-disparate-sample-sizes-tp5727676.html

Hi everyone,

I need advice.  I'm working with a big dataset.

If Population A is 4000 patients and there are 3.2% with the flu, and Population B is 53500 patients and 3.9% have the flu, is the difference in prevalence of the flu significant or not?

The clinic managers are saying use chi square 2x2 table, and then the prevalences are hugely significantly different.  Just in my opinion because of the big sample size difference.  

I'm being conservative and saying with such hugely different sample sizes, it's better to use 3.2/100 versus 3.9/100 so like a z test for proportions for the comparison -- and it's not significant.

Any suggestions greatly appreciated.

Susan