A recent research paper by Jeffrey Clemens of Harvard helps to quantify what might happen if the federal government forbade insurers from taking people’s health into account when deciding whom to cover and how much to charge — but the government did not mandate that everyone had insurance. He finds:

In the early 1990s, several states strictly regulated premiums and product offerings in the markets where small firms and individuals acquire insurance. Within 3 years of adopting these regulations, private coverage of children had fallen by 9 percentage points in the regulated markets relative to equivalent markets in other states (as estimated using the large-group markets within each state as an additional control). Subsequent public insurance expansions covered millions of pregnant women, disabled individuals, and sicker-than-average children. During these expansions, private coverage rates rose by an excess of 7 percentage points in the regulated markets relative to control markets. The analysis reveals an important complementarity between regulations and public insurance: without substantial public insurance programs, strict regulation of premiums and product offerings can lead to significant coverage losses due to adverse selection.

The paper makes a more rigorous version of the point about Massachusetts that’s in my column today. Without a mandate, insurance regulations can sometimes be quite problematic.