Spike in Disease Doesn't Always Mean an Epidemic

Despite Fears Over Rising Numbers, An Increase in Incidence May Be Good

When my wife was in labor in 1991, the doctor attached an electronic fetal monitor to her belly to record her contractions and the baby's heart rate. I remember being so transfixed by the monitor that I forgot about my wife. At one point, she said, "Wow, it hurts." But because the graph on the monitor had yet to rise above the level signaling a contraction, I said, "No, it doesn't."

Even the best data can be subject to misinterpretation.

Americans are confronted every day with graphs, trends, averages and percentages, and few of us have the expertise to grasp them.

"There is terror in numbers," wrote Darrell Huff in his 1954 book "How to Lie With Statistics." If, for example, a small increase in the incidence of a disease over a five-year period is projected out 20 or 30 years, with the same rate of increase, he notes, the disease suddenly looks like an "epidemic," a word scientists use to describe a sudden outbreak of a disease in a discrete population.

Indeed, our child, who was born on the day I incurred my wife's wrath, became part of the so-called autism epidemic.

The autism rate (the number of cases divided by the total population) has gone from fewer than four in 10,000 in 1990 to more than 66 in 10,000 in 2007. Those statistics have led to widespread concern and social traction: a proliferation of advocacy organizations, scores of new, unproven therapies and thousands of lawsuits filed by parents who believe the government's vaccine program is responsible for the higher rates. Between 1997 and 2007, when government funding for most diseases was unchanged, autism funding at the National Institute of Mental Health increased from $22 million to $108 million.

But numbers and rates rise for many reasons. There may actually be more of the disease -- or there may be greater awareness, better detection, improved record-keeping and/or a redefinition of terms.

Panic at the Lab

In 1979, Stuart Gunn, a chemist at Lawrence Livermore National Laboratory in California, died of melanoma, the deadliest form of skin cancer. A year later, a state study found that the rate of melanoma for Livermore employees was five times higher than for residents of surrounding communities. Fear of an epidemic raced through the lab. It did so despite the fact that melanoma had never been linked to any occupational exposure.

The increase was an illusion. In response to Gunn's death, scores of employees went to doctors to have their skin examined, and a few had thin, curable lesions, probably in proportions no higher than would have been found among non-employees -- if they, too, had been seen by a dermatologist. More doctor visits, more biopsies, more cases detected, and soon you had what looked like an epidemic.

Dermatologists report a nearly 300 percent increase in the incidence of melanoma in the last 20 years. Some are convinced there has been a steady increase that began in the 1940s when it became fashionable to have a tan.

But others, such as H. Gilbert Welch, a professor of medicine at Dartmouth Medical School and co-director of the Veterans Affairs Outcomes Group, argue that melanoma is diagnosed earlier because more patients are aware of the sun's dangers, see doctors on a regular basis and get biopsies, and because malpractice insurance companies encourage doctors to do more biopsies. What's more, Welch says, "pathologists are more likely to read a given biopsy as melanoma."