There is an excellent article by Kay Lazar in today's Boston Globe about a perverse result in the Massachusetts insurance market that has been partially responsible for the higher insurance rates in the individual and small business sectors. Here's the lead paragraph:
Thousands of consumers are gaming Massachusetts’ 2006 health insurance law by buying insurance when they need to cover pricey medical care, such as fertility treatments and knee surgery, and then swiftly dropping coverage, a practice that insurance executives say is driving up costs for other people and small businesses.
Wikipedia offers a concise description of this adverse selection problem:
The term adverse selection was originally used in insurance. It describes a situation where an individual's demand for insurance (either the propensity to buy insurance, or the quantity purchased, or both) is positively correlated with the individual's risk of loss (e.g. higher risks buy more insurance), and the insurer is unable to allow for this correlation in the price of insurance.