Sampling bias is a type of selection bias.
Sampling bias is often used when a non-representative subset is used to generalize to a larger group in a study. (ex. testing the effects of high protein diet on patients with renal failure and generalizing to the whole population)
Selection bias is often used when non-equivalent groups are generated in a study and then compared. (ex. testing the effects of cholesterol lowering medication with the control arm having normal serum cholesterol and the experimental arm with hypercholesterolemia)
