In addition, the study revealed unexpectedly high rates of consumers shopping for coverage, something many "experts" predicted wouldn't happen due to the alleged complexity of evaluating insurance plans.

These trends were identified in Rhode Island and Maryland, which require enrollees to actively enroll, as well as the other four states that proffered automatic reenrollment to those with coverage.

"In general, the studied SBMs were successful in retaining a substantial proportion of their 2014 enrollees," the researchers said. "Insurer switching and active reenrollment were both higher than expected in this first year of renewals. Premiums and PTC value maximization were apparently key factors in consumer decision-making. Price sensitivity was particularly important to markets in which the price of the benchmark plan was significantly higher or lower than it was in 2014. Some insurers took advantage of this price sensitivity with aggressive pricing to capture market share, fostering a competitive market in more than half of the studied SBMs, regardless of renewal approach."

Upbeat results notwithstanding, the study authors cautioned that states with their own exchanges will have to keep the pedal to the metal in order to maintain strong exchanges. As affordable coverage continues to drive down the number of Americans who don't have health insurance, the challenge will become retaining more existing exchange consumers and keeping competition healthy so that coverage remains affordable. 

"No reenrollment strategy is perfect, but despite using different methods, all of these states experienced high retention rates in their marketplaces," said Kathy Hempstead, who directs coverage issues at the Robert Wood Johnson Foundation. "It suggests that the most salient factors are the competitiveness of the market and the high value that consumers place on being covered."