Ever pass by a restaurant with less than an “A” rating from the Department of Public Health and make a mental note never to eat there? That letter grade does not tell you how delicious the food is or how attentive the staff is, but at least it hints at the quality of the institution.

In healthcare, people have even less to go on when choosing a doctor than they do when choosing a restaurant. Online reviews might be fake, and higher satisfaction on review sites has even been associated with...