There's a lot of talk these days about comparative effectiveness -- trying to figure out how existing drugs stack up against one another, in an effort to both save money and improve patients' health.

But, as this morning's New York Times notes, a big comparative study of blood pressure medicines published a few years back shows just how tough it can be to persuade docs and patients to change their ways -- particularly if a study shows that an old, cheap drug is better than newer, more expensive options.

The...