Any studies on whether or not insurance mandate = lower premiums?

I know different places have had insurance mandates of various sorts such as for liability for cars as well as heath insurance. I can’t find any decent stuff on in though and I don’t have access anymore to my university’s databases.

Does anyone know of any useful sources on this question?

The thing is that no one is currently suggesting a plan that is equatable to a plan that exists anywhere else.

The closest case would be Mass. requirement for insurance. In Mass, costs for consumers went up 23-56%.
(Victoria Bunce and J. P. Wieske, “Health Insurance Mandates in the States 2008,” Council for Affordable Health Insurance, pp. 4–7.)

In fairness, this is not as bad as it looks. Premiums went up for all americans in that timeframe.