A study looks a the problems with relying on quality data:

In an accompanying editorial, Sean Michael O’Brien, Ph.D., and Eric D. Peterson, M.D., both of Duke University, said the findings add to the “sobering picture” for patients who try to use available quality rating information.

“Most [rating] systems seem to do a reasonable job at identifying groups of hospitals that perform well on average, yet there is considerable uncertainty regarding the true performance of a particular hospital,” they wrote.

“As noted, some truly exceptional hospitals will be improperly rated as poor whereas some mediocre hospitals will be rated as excellent,” they continued.