Katherine Carpenter couldnt sleep. For more than a week shed been coughing herself awake every night and then hacking until she retched. Finally, she decided to see a doctor.

The physician suspected bronchitis and wrote Carpenter a prescription for heavy-duty cough medicine. She also suggested antibiotics. Thats pretty standard: Up to 80 percent of people who go to a physician for acute bronchitis are prescribed antibiotics. But Carpenter, an import entry agent for UPS, didnt want antibiotics. She thought theyd stop working if you take them too often, and she suspected her symptoms were caused by a virus, which antibiotics dont affect anyway.

She didnt know it, but her hesitation had science on its side: A meta-analysis in the Cochrane Database of Systematic Reviews looked at 17 trials on antibiotics for people with acute bronchitis, and concluded that they only slightly shorten the duration of the illnessif they have any benefit at all. (And of course theres the issue of antibiotic resistance to consider.) In the end, Carpenter refused the prescription, and her bronchitis eventually cleared up. But the experience left her with the distinct impression that she was just one more patient on the medical assembly line. I felt like a number, she says.

Instead of being a number, Carpenter might have preferred to see a number, one that can help us weigh the benefits (or lack thereof) of a treatment. That number exists, and its called the number needed to treat. Developed by a trio of epidemiologists back in the 80s, the NNT describes how many people would need to take a drug for one person to benefit. (The NNT for antibiotics in a case of acute bronchitis is effectively infinity, because the medicine is no better at curing the illness than a placebo.)

Consider a couple other examples: If your kid is throwing up and you take her to the hospital, she might get a drug called Zofran. The NNT for that is 5, meaning that only five kids need to take Zofran for one of them to stop throwing up. And if you look at Zofrans number needed to harm (the number of people who would need to take a drug for one to have a bad side effect) the answer is well, there really isnt oneno one has a significant side effect.

Now, say youre pushing 50. Youre healthy, but your doctor suggests you start taking a baby aspirin. Just in case, you know? That NNT is 2,000. Thats how many people have to take a daily aspirin for one (nonfatal) heart attack to be prevented. Statistically speaking: Not especially helpful.

Its unfortunate, then, that the NNT is not a statistic thats routinely conveyed to either doctors or patients. But you can look it up on a site that youve probably never heard of: TheNNT.com. Started by David Newman, a director of clinical research at Icahn School of Medicine at Mount Sinai hospital, the sites dozens of contributors analyze the available studies, crunch the numbers on benefits and harms, and then post the results. While a low NNT is generally good and a high NNT is bad, you also have to consider the severity of both the illness and the drugs side effects. Which is why the team added a color-coding system: Green for when a treatment makes sense, yellow for when more study is needed, red for when the harms and the benefits cancel each other out, and black when the harms outweigh the benefits.

Newmans goal for the site is nothing short of a revolution in medical practice. He wants doctors to base their treatments on good scientific evidence, not tradition, hunch, and the fear that patients will see them as doing nothing. And he wants patients to start demanding such care. Thats the big picture, anyway. For now, hed be happy if he could just get people looking at medicine in a different way. People tend to think that if its a medical intervention, theres science behind it, he says. Unfortunately, thats often not the case. It is a lie to tell patients to do something without telling them, You should know weve done lots of research on this and we cant find any benefit to it.

Its a bright, cold morning outside Mount Sinai Hospital in New York City. Central Park is across the street, and runners huff along the paths, baby joggers in front, dogs in tow. Newman has just arrived at work in the emergency department where hes an attending physician, and hes giving his residents the Three Networks spiel.

ABC, always be closing. You want to be moving patients back home or into the hospital for treatment. At the ER, the front door is always open, but if the back door is closed, and you have people mounting up, things get missed, heart attacks occur, sepsis gets worse, and people die. Always be closing. Then comes NBC, never be consultingdont call specialists if you can avoid it. Then CBS, close before signoff. Theres good evidence that medical errors are more likely to occur with handoffs. Discharge your cases before the end of your shift to avoid these errors, he tells his charges.

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This Mans Simple System Could Transform American Medicine