Here is a link to the article from the Journal of the American Medical Association (JAMA). The study finds a positive correlation between a plan’s star rating and the likelihood of a Medicare beneficiary to enroll in a plan. For new to Medicare advantage, a 1-star rating increase resulted in a 9.5% increase in likelihood to enroll. For switchers, a 1-star rating increase resulted in a 4.4% increase in likelihood to enroll.
It is not clear whether the Medicare beneficiary actually used the CMS star rating as a part of their evaluation process. It could be that plans with higher star ratings have better reputations, etc., which make them more popular. CMS is spending a considerable amount of money and effort promoting the star ratings. Additionally, CMS is providing bonus payments to plans with star ratings of at least 4 stars and higher. Starting in 2014, plans with less than 4 stars will get no bonuses, so this should increase the tendency toward higher star rated plans.