@stefanforfan if you use NHANES, I've seen HDL cholesterol as predicted by BMI to be non-linear in a few years
@PausalZ That's actually a nice example although there's a lot of residual variation. But I think this might do the job, thanks!
@stefanforfan yeah, unfortunately the residual variation makes it hard to visually see. I suspect most relevant public health examples will have this same issue...
However, you could also view that as a benefit (i.e., we should use splines because a scatterplot may not be enough)
@PausalZ Yeah, that's a good point.
@stefanforfan here is 2017-2018 with LOESS (x: BMI, y: HDL)