I'm trying to fit a linear mixed-effects model with fitlme, e.g.: quadmdl = fitlme(Data,'DV ~ X1^2 + (1 + X1^2 | Subject)');
This models fixed effects for both X1 and X1^2, but I only want to model X1^2. In other words, I want my model to have the quadratic (second-order) term without the linear (first-order) one: DV ~ X1^2 + (1 + X1^2 | Subject) as opposed to DV ~ X1 + X1^2 + (1 + X1 + X1^2 | Subject).
Is there a way to specify this in the model?