My data is made up of 4 groups, each with a large and identical sample size of 20,000. The number of successes in each group is fairly small:
Group A B C D Sample 20,000 20,000 20,000 20,000 Successes 90 120 110 200 Pr(Success) 0.5% 0.6% 0.6% 1.0%
I've done a simple chi-square test and found a significant difference (hope that was right!). Is it now appropriate to then do t-tests or are the proportions too small and I should do a series of further chi-squared tests? (I'm generally unsure about if/ when t-test is appropriate for very small. large proportions even if np and nq >20).