A new and relatively expensive medication is released into the population to treat type II diabetes. A doctor notices that poor patients are less likely to see effects from the medication than more wealthy patients, but after conducting a survey the doctor finds the poor patients are less likely to fully comply with their medication regimen because they cannot afford to take the medication on a regular basis. This is an example of which of the following?

A) Confounding

B) Statistical interaction

C) Selection bias

D) Recall bias