I have results from three archaeological populations in which I found that the prevalence of a certain disease was:
65% (13/20) in population A,
31.25% (5/16) in population B and
46.60% (48/103) in population C
I did a chi-squared test and found that while population A was significantly more affected than population B (χ2 = 4.05, df=1, P= 0.04), population A was not significantly more affected than population C (χ2 = 2.27, df=1, P= 0.13)
However, I then learned that you can test each population (2x1 contingency table) to see if its results are significant. The sample sizes are quite small and these tests have shown that the results from each population are not significant (e.g. SPSS tells me that the fact that 5 out of 16 individuals were affected by disease in population B is not significant: χ2 = 1.80, df=1, P= 0.18) . Does then render the comparison of populations meaningless?