Hello!

I have non-linear data (growth) and I would like to compare growth curves between two populations - does one population get bigger at a younger age?

I have read that I may be able to compare the elevations using an ANCOVA but including a quadratic term as a main effect and as an interaction such that:

x=age; y=size variable; 2 populations

size variable >= population; age; age^2; population*age population*age^2

However, I have been unable to figure out how to get an interaction in ANCOVA (using both GRM and GLZ). I'm only getting results for the main effects

Q1: is this an appropriate way of comparing 2 curves?

Q2: How can I get an ANCOVA to assess the interaction of my main effects?

I'm using v10

Thanks!