Suppose That to Estimate the Effect of Medicaid on Health

Suppose that to estimate the effect of Medicaid on health status,a researcher compares those who choose to enroll in the program to those who are not enrolled.Which of the following would cause the resulting estimate to be biased?

A) Eligibility for Medicaid is established by factors that might also affect health.
B) Eligibility for Medicaid is established by factors that do not affect health.
C) Those who enroll in Medicaid are likely to receive more access to medical care than those who do not enroll.
D) Access to health care is likely to have a significant impact on an individual's overall health.