A generation ago, depression was viewed as an unwanted guest: a gloomy presence that might appear in the wake of a loss or a grave disappointment and was slow to find the door. The people it haunted could acknowledge the poor company — I’ve been a little depressed since my father died — without worrying that they had become chronically ill.

Today, the condition has been recast in the medical literature as a darker, more permanent figure, a monster in the basement poised to overtake the psyche. For decades, researchers have debated the various types of depression, from mild to severe to “endogenous,” a rare, near-paralyzing despair. Hundreds of studies have been conducted, looking for markers that might predict the course of depression and identify the best paths to recovery. But treatment largely remains a process of trial and error. A drug that helps one person can make another worse. The same goes for talk therapies: some patients do very well, others don’t respond at all.

“If you got a depression diagnosis, one of the most basic things you want to know is, what are the chances of my life returning to normal or becoming optimal afterward?” said Jonathan Rottenberg, a professor of psychology at the University of South Florida. “You’d assume we’d have an answer to that question. I think it’s embarrassing that we don’t.”

In a paper in the current issue of Perspectives on Psychological Science, Dr. Rottenberg and his colleagues argue that, in effect, the field has been looking for answers in the wrong place. In trying to understand how people with depression might escape their condition, scientists have focused almost entirely on the afflicted, overlooking a potentially informative group: people who once suffered from some form of depression but have more or less recovered.