For explanatory purposes, I will give a fake example to understand my question (and goal). Let's suppose I get from different published papers data about the concentration of a substance (
subst.concent) depending on age (
age) and if they are smokers or non-smokers (
smoking). Following this example, I find that for
smokers, the concentration of that substance increase as age increase, while for
non-smokers there is no effect. Here a graph of what I find with my actual data (but modified to the "smokers" example):
I would like to test the effect of both
subst.concent. I would expect to find a significant interaction between
smoking. I tried a linear regression using the mean of each "population", however, I don't think this is the most appropriate since it doesn't consider the SD and for instance, the model gives an
R² of 1, when I guess all the variance is not explained by my two variables.
How could I test the
smoking effect in my
subst.concent and the magnitude of their effect using both the mean and the SD?
Thanks in advance!!!