The Impact of Market Share on Health Insurance Premiums

It is usually argued that market concentration leads to higher prices. This well-known proposition has led to concern about the level of concentration in state health-insurance markets, since the largest insurer in many states has a market share greater than 50 %. Moreover, the data compiled by the American Medical Association indicates that insurance markets have become more concentrated over the last ten years. Thus, some have suggested that health insurance premiums would decrease significantly if state markets were made more competitive. This paper explores that proposition through a computational model and an empirical analysis of the relationship between the market share of the largest firm in a state and the average health insurance premium in that state.