Problem: I use a common clinical specimen divided equally into two sets with each set to test 3 culture media for growth of a certain organism after processing. The 1st is processed by method A. The 2nd processed by method B. After processing, inoculation to 3 media each was done for the testing.

Schematically: Specimen ---> 1/2 processed by method A, 1/2 processed by method B;
Processed specimen A ---> inoculated to medium A, B and C; Processed specimen B ---> inoculated to medium A, B and C. Proportions of positive growth in each media is determined then compared.

What's the formula I would use? What is it called? In addition: What software can I use that's available for this? Please indicate if free or not and also the link if online.

I really appreciate any help or guidance. Thanks in advance.