The addition of a single insurer in a county was associated with a 1.2% lower premium for the average silver plan and a 3.5% lower premium for the benchmark plan in the federally run Health Insurance Marketplaces for 2015, according to a study published today in Health Affairs. The authors, from the Agency for Healthcare Research and Quality and Congressional Budget Office, said the findings suggest that increased insurer participation in the Marketplaces reduces federal payments for premium subsidies, which are tied to the cost of the benchmark plan (the second-lowest-cost silver plan). “As policy makers consider further legislative or regulatory changes to the Marketplaces, it will be important to consider the likely impact of any such change on insurer participation and the subsequent effect on overall premiums and federal costs,” they said.