Defining "Streetlight" Research

In my last post (“Quality and Chronic Disease Management”) I use the term “streetlight” research without defining it, so I thought that I should do that. It is based on an old joke:

A guy is walking down the street one night a finds another guy on his hands and knees searching in the gutter under a streetlight. He asks what he is doing, and the second guy says “I dropped my car keys.” So the first guy offers to help, but after some time they are unsuccessful, so he asks “Where exactly did you drop them?”
“Down the block,” the second guy says, pointing.
“So why are we looking here?” the other asks in exasperation.
“Well,” the second guy replies, “the light’s better!”

Thus:
Streetlight research. You do the research that it seems feasible (cost, effort) even though it may not answer the real question that you have. (“Well, that would be much too difficult a study to do.”) It can get published, get you promoted, and even get you famous, but it still doesn’t answer the question you originally had.