t-test for sample comparison

Rick Parcels kenzie71 at pathcom.com
Sat Nov 15 00:13:22 EST 1997


I have to perform the preparatory test to the microbial limits test (USP)
on all of my company's final products.  The method I would like to use to
validate the test is as follows:

Broth/Product mixture is inoculated with 10-100cfu/mL.  Mixture is plated
10 times using 1.0 mL.  Counts are taken.

Broth/Water mixture is inoculated with 10-100cfu/mL.  Mixture is plated 10
times using 1.0 mL.  Counts are taken.

These results from these two mixtures (Product and Control) are compared
using a t-test.

Does anyone know if the t-test is the appropriate statistical method to be
using to comapre the results?  I learned in school that the t-test can only
be used if the larger variance divided by the smaller variance is < 2.  My
ratio is much larger than two.  I can't find any other appropriate method
of comparing two population means (or would this be a sample mean?).





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