A survey of 334 seniors who purchased private Medicare supplemental plans in previous years using a health insurance exchange revealed that 63 percent reevaluated their coverage during the 2012 Medicare Annual Enrollment Period, which ended Dec. 7, 2011. Of those who reevaluated, 31 percent bought different plans.

When asked why they reevaluated their coverage, respondents' top three responses were: "I wanted to confirm that I have the best coverage for me" (43 percent); "My premiums increased" (23 percent); and "My out-of-pocket expenses increased" (7 percent). A third (33 percent) said they renewed their existing plans without reevaluating and 3 percent said they purchased private Medicare plans for the first time. Less than 1 percent discontinued existing coverage without replacing it.

The survey was fielded from Dec. 20-26, 2011, by Extend Health Inc., which operates the nation's largest private Medicare exchange.