Hello! I am currently doing my Extended Essay for Biology and I am not sure what stat test to use for my results. I am comparing audio frequency with the rate of antennal activity of the pill bug. I have found that from 0 Hz, the antennal movement also increases up to 400 Hz where it peaks and thereafter, as the frequency goes higher, the antennal movement would decrease. I have 6 samples (controlled aka 0Hz, 400Hz, 1500Hz, 3000Hz, 4000Hz, 5000Hz) and I have tried the Spearman's rank correlation so far but it gave me a -0.14 correlation since it was not linear. I also tried the student t test, but from what i know, it does not seem to be valid in this experiment. Does the two sample means have to be within the same units of measurement to actually be compared in a T-test? Or can I compare frequency (hz) and # of antennal twitches with the t-test? I am looking into quadratic regression stats at the moment, but I am quite confused as to what regression is and whether or not it is the same as "correlation"? The format appears similar to the spearman's test, but is it the same? Thank you!