As it is, the longevity gap starts at birth and persists through middle age, but then it eventually disappears. If you reach 80 in the United States, your life expectancy is longer than in most other developed countries. The United States is apparently doing something right for its aging population, but what?

Image Credit... Viktor Koen

One frequent answer has been Medicare. Its universal coverage for people over 65 has often been credited with shrinking the longevity gap between the United States and other developed countries.

But when Dr. Preston and a Penn colleague, Jessica Y. Ho, looked at mortality rates in 1965, before Medicare went into effect, they found an even more pronounced version of today’s pattern: middle-aged people died much more often in the United States than in other developed countries, but the longevity gap shrunk with age even faster than today. In that pre-Medicare era, an American who reached 75 could expect to live longer than most people elsewhere.

Besides smoking, there could be lots of other reasons that Americans are especially unhealthy in middle age. But Dr. Preston says he saw no evidence for the much-quoted estimates that poor health care is responsible for more preventable deaths in the United States than in other developed countries. (Go to nytimes.com/tierneylab for details.)

For all its faults, the American system compares well by some important measures with other developed countries, as Dr. Preston and Ms. Ho enumerate. Americans are more likely to be screened for cancer, and once cancer is detected, they are more likely to survive for five years.

It’s been argued that the survival rate for cancer appears longer in America merely because the disease is detected earlier, but Dr. Preston says that earlier detection can be an advantage in itself, and that Americans might also receive better treatment. He and Ms. Ho conclude that the mortality rates from breast cancer and prostate cancer have been declining significantly faster in the United States than in other industrialized countries.

Americans also do relatively well in surviving heart attacks and strokes, and some studies have found that hypertension is treated more successfully in the United States. Compared with Europeans, Americans are more likely to receive medication if they have heart disease, high cholesterol, lung disease or osteoporosis.