I'm an undergrad doing an internship in a lab. My statistics background is very poor. I pretty much know what analysis to do on my experiments only because I read this, and I have statistical software that I command 'do a t-test pls'.
I'm studying memory, I measure the escape response of the animal, if the escape response is significantly lower than in testing, I can say there is memory. Here is what I can do with my data.
a) On most of the experiments homoscedasticity assumption is violated, so I do non-parametric t-student if there are two groups, or non-parametric anova is >3 groups. Let's say there are two groups, Control and Trained, I find that the Trained group has a significantly lower escape response (comparing the mean of CT vs the mean of TR), the experiment went how it was supposed to do and everyone is happy.
b) Same situation but, even though I can see a tendency, the difference is not statically significant (what happens most of the time). What I was told to is to relativize the data. How I do that? For each animal I take my Testing observation and I divide it by the maximum observation I have of THAT animal (the maximum can be observed in either training or testing, I expect the maximum of my control groups to be on the testing session, and the maximum of my trained group on the training session). So, the relativized score is TS/Max. I then do the anova/t-student and the tendency I saw on the raw scores is now statically significant.
Now, there is some argue in the lab about doing that. There is no doubt that from a biological perspective there is no problem in doing that. But on the statistics front, some people say you shouldn't, some people say it's fine (most people of the lab are biologists, but we consulted with statisticians)
What I'm asking Can I do a linear regression, where instead of having one observation for each animal (the testing raw score) I add a (moderator? mediator?) variable, the maximum it got on either training/testing?
Thanks in advance, I'll happily respond if anything is not clear (sorry, english is not my mother tongue) and I can provide a data set if needed.