Deciding where to seek treatment might seem simple for a German diagnosed with prostate cancer. The five-year survival rate hardly varies from one clinic to the next: All bunch around the national average of 94 percent. Health care providers in Germany, and elsewhere, have usually been judged only by broad outcomes such as mortality.

But to patients, good health means more than life or death. Thanks to a study in 2011 by Germany's biggest insurer, a sufferer now knows that the national average rate of severe erectile dysfunction a year after removal of a cancerous prostate gland is 76 percent — but at the best clinic, it's just 17 percent. For incontinence, the average is 43 percent; the best, 9 percent. But such information is the exception in Germany and elsewhere, not the rule.

What matters to patients should also matter to policymakers. Side effects such as erectile dysfunction and incontinence are not only unpleasant, but expensive to treat. And measuring outcomes is the first step to choosing the best treatments and providers at the lowest prices. But few places do this well, says Michael Porter of Harvard Business School.

Doctors and administrators have long argued that tracking patients after treatment would be too difficult and costly, and unfair to providers lumbered with particularly unhealthy patients. But better sharing of medical records and a switch to holding them electronically mean that such arguments are now moot. Risk-adjustment tools cut the chances that providers are judged on the quality of their patients, not their care.

In theory, national health care systems should find measuring outcomes easier. Britain's National Health Service compiles masses of data. But it stores most data by region or clinic, and rarely tracks individual patients as they progress through treatment. Sweden's quality registries do better. They analyze long-term outcomes for patients with similar conditions, or who have undergone the same treatment. Some go back to the 1970s and one of the oldest keeps records of hip replacements, letting medics compare the long-term performance of procedures and implants. Sweden now has the world's lowest failure rate for artificial hips.

Elsewhere, individual hospitals are blazing a trail. Germany's Martini-Klinik uses records going back a decade to fine-tune its treatment for prostate problems. The Cleveland Clinic, a nonprofit outfit specializing in cardiac surgery, publishes a wide range of outcome statistics; it now has America's lowest mortality rate for cardiac patients.

And though U.S. politicians flinch at the term "cost-effectiveness," some of the country's private health firms have become statistical whizzes. Kaiser Permanente, which operates in nine states and Washington, D.C., pools the medical records for all its centers and, according to McKinsey, a consultancy, has improved care and saved $1 billion as a result.

Such approaches are easiest in fields such as prostate care and cardiac surgery, where measures for quality-of-life are clear. But some clinics have started to track less obvious variables, such as how soon after surgery patients get back to work. It's new ground for doctors, who have long focused on clinical outcomes only.

Copyright 2013 The Economist Newspaper Limited, London. All Rights Reserved. Reprinted with permission.