Accounting for body-size in morphological data sets can be solved by using the residuals of simple linear regression with the trait~body-size.
But I've been getting some annoying results using this method, and was wondering whether another method would give more realistic results.
Let's start with two species that look different, one is larger and has short femurs, while the other is small with long femurs:
svl=c(24,26,14,26,27,19, 42,46,45,37,59,48), femur=c(12,14,8,13,14,9, 14,15,16,12,19,17), sp=c("a","a","a","a","a","a","b","b","b","b","b","b")
Below shows original data, then the corrected by linear regression and division by body-size.
My point here: Because of the range in size, the regression correction has predicted that the corrected femur length is not different between species. And yet when I created the data I specifically made sp A femur 1/2 of body size and sp B 1/3 of body size.
So: should I just stick to dividing by body-size to correct other morphological traits? Or is there a better modelling solution?