Every illness is a story, and Annie Page’s began with the kinds of small, unexceptional details that mean nothing until seen in hindsight. Like the fact that, when she was a baby, her father sometimes called her Little Potato Chip, because her skin tasted salty when he kissed her. Or that Annie’s mother noticed that her breathing was sometimes a little wheezy, though the pediatrician heard nothing through his stethoscope.

The detail that finally mattered was Annie’s size. For a while, Annie’s fine-boned petiteness seemed to be just a family trait. Her sister, Lauryn, four years older, had always been at the bottom end of the pediatrician’s growth chart for girls her age. By the time Annie was three years old, however, she had fallen off the chart. She stood an acceptable thirty-four inches tall but weighed only twenty-three pounds—less than ninety-eight per cent of girls her age. She did not look malnourished, but she didn’t look quite healthy, either.

“Failure to thrive” is what it’s called, and there can be scores of explanations: pituitary disorders, hypothyroidism, genetic defects in metabolism, inflammatorybowel disease, lead poisoning, H.I.V., tapeworm infection. In textbooks, the complete list is at least a page long. Annie’s doctor did a thorough workup. Then, at four o’clock on July 27, 1997—“I’ll never forget that day,” her mother, Honor, says—the pediatrician called the Pages at home with the results of a sweat test.

It’s a strange little test. The skin on the inside surface of a child’s forearm is cleaned and dried. Two small gauze pads are applied—one soaked with pilocarpine, a medicine that makes skin sweat, and the other with a salt solution. Electrodes are hooked up. Then a mild electric current is turned on for five minutes, driving the pilocarpine into the skin. A reddened, sweaty area about an inch in diameter appears on the skin, and a collection pad of dry filter paper is taped over it to absorb the sweat for half an hour. A technician then measures the concentration of chloride in the pad.

Over the phone, the doctor told Honor that her daughter’s chloride level was far higher than normal. Honor is a hospital pharmacist, and she had come across children with abnormal results like this. “All I knew was that it meant she was going to die,” she said quietly when I visited the Pages’ home, in the Cincinnati suburb of Loveland. The test showed that Annie had cystic fibrosis.

Cystic fibrosis is a genetic disease. Only a thousand American children per year are diagnosed as having it. Some ten million people in the United States carry the defective gene, but the disorder is recessive: a child will develop the condition only if both parents are carriers and both pass on a copy. The gene—which was discovered, in 1989, sitting out on the long arm of chromosome No. 7—produces a mutant protein that interferes with cells’ ability to manage chloride. This is what makes sweat from people with CF so salty. (Salt is sodium chloride, after all.) The chloride defect thickens secretions throughout the body, turning them dry and gluey. In the ducts of the pancreas, the flow of digestive enzymes becomes blocked, making a child less and less able to absorb food. This was why Annie had all but stopped growing. The effects on the lungs, however, are what make the disease lethal. Thickened mucus slowly fills the small airways and hardens, shrinking lung capacity. Over time, the disease leaves a child with the equivalent of just one functioning lung. Then half a lung. Then none at all.

The one overwhelming thought in the minds of Honor and Don Page was: We need to get to Children’s. Cincinnati Children’s Hospital is among the most respected pediatric hospitals in the country. It was where Albert Sabin invented the oral polio vaccine. The chapter on cystic fibrosis in the “Nelson Textbook of Pediatrics”—the bible of the specialty—was written by one of the hospital’s pediatricians. The Pages called and were given an appointment for the next morning.

“We were there for hours, meeting with all the different members of the team,” Honor recalled. “They took Annie’s blood pressure, measured her oxygen saturation, did some other tests. Then they put us in a room, and the pediatrician sat down with us. He was very kind, but frank, too. He said, ‘Do you understand it’s a genetic disease? That it’s nothing you did, nothing you can catch?’ He told us the median survival for patients was thirty years. In Annie’s lifetime, he said, we could see that go to forty. For him, he was sharing a great accomplishment in CF care. And the news was better than our worst fears. But only forty! That’s not what we wanted to hear.”

The team members reviewed the treatments. The Pages were told that they would have to give Annie pancreatic-enzyme pills with the first bite of every meal. They would have to give her supplemental vitamins. They also had to add calories wherever they could—putting tablespoons of butter on everything, giving her ice cream whenever she wanted, and then putting chocolate sauce on it.

A respiratory therapist explained that they would need to do manual chest therapy at least twice a day, half-hour sessions in which they would strike—“percuss”—their daughter’s torso with a cupped hand at each of fourteen specific locations on the front, back, and sides in order to loosen the thick secretions and help her to cough them up. They were given prescriptions for inhaled medicines. The doctor told them that Annie would need to come back once every three months for extended checkups. And then they went home to start their new life. They had been told almost everything they needed to know in order to give Annie her best chance to live as long as possible.

The one thing that the clinicians failed to tell them, however, was that Cincinnati Children’s was not, as the Pages supposed, among the country’s best centers for children with cystic fibrosis. According to data from that year, it was, at best, an average program. This was no small matter. In 1997, patients at an average center were living to be just over thirty years old; patients at the top center typically lived to be forty-six. By some measures, Cincinnati was well below average. The best predictor of a CF patient’s life expectancy is his or her lung function. At Cincinnati, lung function for patients under the age of twelve—children like Annie—was in the bottom twenty-five per cent of the country’s CF patients. And the doctors there knew it.

It used to be assumed that differences among hospitals or doctors in a particular specialty were generally insignificant. If you plotted a graph showing the results of all the centers treating cystic fibrosis—or any other disease, for that matter—people expected that the curve would look something like a shark fin, with most places clustered around the very best outcomes. But the evidence has begun to indicate otherwise. What you tend to find is a bell curve: a handful of teams with disturbingly poor outcomes for their patients, a handful with remarkably good results, and a great undistinguished middle.

In ordinary hernia operations, the chances of recurrence are one in ten for surgeons at the unhappy end of the spectrum, one in twenty for those in the middle majority, and under one in five hundred for a handful. A Scottish study of patients with treatable colon cancer found that the ten-year survival rate ranged from a high of sixty-three per cent to a low of twenty per cent, depending on the surgeon. For heartbypass patients, even at hospitals with a good volume of experience, risk-adjusted death rates in New York vary from five per cent to under one per cent—and only a very few hospitals are down near the one-per-cent mortality rate.

It is distressing for doctors to have to acknowledge the bell curve. It belies the promise that we make to patients who become seriously ill: that they can count on the medical system to give them their very best chance at life. It also contradicts the belief nearly all of us have that we are doing our job as well as it can be done. But evidence of the bell curve is starting to trickle out, to doctors and patients alike, and we are only beginning to find out what happens when it does.

In medicine, we are used to confronting failure; all doctors have unforeseen deaths and complications. What we’re not used to is comparing our records of success and failure with those of our peers. I am a surgeon in a department that is, our members like to believe, one of the best in the country. But the truth is that we have had no reliable evidence about whether we’re as good as we think we are. Baseball teams have win-loss records. Businesses have quarterly earnings reports. What about doctors?

There is a company on the Web called HealthGrades, which for $7.95 will give you a report card on any physician you choose. Recently, I requested the company’s report cards on me and several of my colleagues. They don’t tell you that much. You will learn, for instance, that I am in fact certified in my specialty, have no criminal convictions, have not been fired from any hospital, have not had my license suspended or revoked, and have not been disciplined. This is no doubt useful to know. But it sets the bar a tad low, doesn’t it?

In recent years, there have been numerous efforts to measure how various hospitals and doctors perform. No one has found the task easy. One difficulty has been figuring out what to measure. For six years, from 1986 to 1992, the federal government released an annual report that came to be known as the Death List, which ranked all the hospitals in the country by their death rate for elderly and disabled patients on Medicare. The spread was alarmingly wide, and the Death List made headlines the first year it came out. But the rankings proved to be almost useless. Death among the elderly or disabled mostly has to do with how old or sick they are to begin with, and the statisticians could never quite work out how to apportion blame between nature and doctors. Volatility in the numbers was one sign of the trouble. Hospitals’ rankings varied widely from one year to the next based on a handful of random deaths. It was unclear what kind of changes would improve their performance (other than sending their sickest patients to other hospitals). Pretty soon the public simply ignored the rankings.

Even with younger patients, death rates are a poor metric for how doctors do. After all, very few young patients die, and when they do it’s rarely a surprise; most already have metastatic cancer or horrendous injuries or the like. What one really wants to know is how we perform in typical circumstances. After I’ve done an appendectomy, how long does it take for my patients to fully recover? After I’ve taken out a thyroid cancer, how often do my patients have serious avoidable complications? How do my results compare with those of other surgeons?

Getting this kind of data can be difficult. Medicine still relies heavily on paper records, so to collect information you have to send people to either scour the charts or track the patients themselves, both of which are expensive and laborious propositions. Recent privacy regulations have made the task still harder. Yet it is being done. The country’s veterans’ hospitals have all now brought in staff who do nothing but record and compare surgeons’ complication rates and death rates. Fourteen teaching hospitals, including my own, have recently joined together to do the same. California, New Jersey, New York, and Pennsylvania have been collecting and reporting data on every cardiac surgeon in their states for several years.

One small field in medicine has been far ahead of most others in measuring the performance of its practitioners: cystic-fibrosis care. For forty years, the Cystic Fibrosis Foundation has gathered detailed data from the country’s cystic-fibrosis treatment centers. It did not begin doing so because it was more enlightened than everyone else. It did so because, in the nineteen-sixties, a pediatrician from Cleveland named LeRoy Matthews was driving people in the field crazy.

Matthews had started a cystic-fibrosis treatment program as a young pulmonary specialist at Babies and Children’s Hospital, in Cleveland, in 1957, and within a few years was claiming to have an annual mortality rate that was less than two per cent. To anyone treating CF at the time, it was a preposterous assertion. National mortality rates for the disease were estimated to be higher than twenty per cent a year, and the average patient died by the age of three. Yet here was Matthews saying that he and his colleagues could stop the disease from doing serious harm for years. “How long [our patients] will live remains to be seen, but I expect most of them to come to my funeral,” he told one conference of physicians.