Hi All, my data looks like this:
Treated (4 replicates): (1) 21 positive, 178 negative (10.55% positive), (2) 25+, 166- (13.09% +), (3) 25+, 185- (11.9% +) and (4) 7+, 53- (11.67% +)
Non-Treated (3 replicates): (1) 131 positive, 1285 negative (9.25% positive), (2) 133+, 1264- (9.25% +), (3) 139+, 1368- (9.22% +)
I want to know if there's any significant difference between treated and non-treated.
I could either do a chi-square for each replicates against one of the non-treated, so that the 2x2 table would look like this:
Treatment: 21+ 178-
Non-treatment: 131+ 1285-
or I could do a student's t test, in which I first calculate the mean % positive for all 4 treated samples, and compare it against the mean % positive for all 3 non-treated samples.
The problem: Results are non-significant with chi-square but they are with student's t test. I am of course very tempted to use the latter test, but I would also like to confirm with experts here that it's correct for me to do so. I know that the 2 tests are investigating slightly different questions (chi-square: association between treatment and outcome and student's t test: difference between means). But from a biologist's point of view, the distinction is not that clear. Please advise.