Guidance with piecewise linear data set I have data that looks like:

As you can see my linear modeling doesn't really work since the y values increase and then stay constant. I want to separate my data for each group into 2 and then perform linear regression on both but the cutoff point is also unknown. How can I go about modelling such phenomena I have no idea?

Try modeling with linear splines where the knots are a part of optimization, so you may need nonlinear regression
