I have 2 columns of of the concentration of fat in fish which is measured by 2 different labs. I need to know if the difference of the results from these 2 labs are statistically significant. The data are collected from measurement of fat in 34 identical fish samples.
The problem is that these 34 samples consist of 3 types of fish, and each type accumulates different amount of fat averagely. Is there any sensitive method to take the influence pf fish types into consideration?
One idea came in my mind is to subtract one of the groups from the other one and run a t-test, one sample, with a hypothetical mean value=0. Would that make sense?