I'm trying to study how age as a confounder may affect the relationship between commute mode and BMI (and design a research proposal).
To explain age as a potential confounder, I compared age to commute mode and then age to BMI. I found a weak association between age and BMI in my data.
In the literature does anyone know if BMI is expected to change with age? Is there a linear/ other relationship form? Please could someone attach any papers/ links for help.
Also, does anyone know what a clinically meaningful BMI is too? Would a change of 1-2 be important?