<http://www.talkstats.com/threads/is-chi-sqaure-the-right-test-for-analysing-these-disease-test-results.23132/>
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"Hi All!\r\n\r\nI have three tests testing for three different strains of the same disease. Unfortunately the tests are not very specific since antibodies (and therefore positive results) to the three strains are common in most populations. If however, there is a true outbreak of the disease, then of the strains will typically have a much higher population prevalence than the other two.\r\n\r\nWe take many batches of samples from different populations to see if there is a dominant strain (and therefore outbreak of that strain.)\r\n\r\nA sample of my data can look like this:\r\n\r\nSample size: 100 individuals\r\nPositives for test1: 24/100\r\nPositives for test2: 42/100\r\nPositives for test3: 18/100\r\n\r\nThe question is now whether the apparent higher levels for test2 (equals strain 2 of the disease) is due to true disease or just chance. I've used a chi-squared test on the data and am very happy with my results (the stats confirm my intuition.) However, I am not sure if a chi-squared test is allowed, because my results are not independent. For example one individual can test positive for 1, 2 or 3 three of the different strains.\r\n\r\nThanks to all the helpful people out there!\r\n\r\nJohann"
<https://www.talkstats.com/threads/is-chi-sqaure-the-right-test-for-analysing-these-disease-test-results.23132/>