The researchers examined the effects of tiered physician networks introduced in six health plans offered to beneficiaries of the Massachusetts Group Insurance Commission (GIC). Specifically, they (1) determined whether tier status of a regular physician is associated with choice of plan; (2) determined whether tier status affects the probability that a patient will visit a physician for the first time; (3) determined whether tier status affects the probability that a patient will continue seeking care with a physician seen prior to tiering; and (4) identified patient, plan, and physician characteristics associated with greater responsiveness on aims 1-3. The objective of this project was to assist employers in assessing the impact of physician tiering on consumer behavior and to assess the value of this benefit design feature.