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What if we’re all wrong? What if prevention doesn’t save money?

I’ve spent a good part of this week making my way through “Prevention vs. Treatment,” a new book edited by Halley Faust, president-elect of the American College of Preventive Medicine, and Pacific Lutheran University’s Paul Menzel. The entire volume is a worthy read for anyone interested in how we prioritize spending in health care chapter. A chapter by Louise Russell of Rutgers University stands out in challenging much of our political and policy discourse around preventive health.

Russell is an economist by training who has written extensively on cost-effectiveness in health care. She co-chaired the U.S. Public Health Panel on Cost-Effectiveness in Health and Medicine in the mid-1990s, and she serves as an elected member of the Institute of Medicine. In this chapter, she draws heavily on research of Tufts’ Joshua Cohen, who crunched the numbers on the cost-effectiveness of 279 interventions that range from colonoscopies to smoking cessation programs.

Only 20 percent of those regularly used preventive measures are “cost saving,” reducing costs while improving the quality of health, the research found. The rest tend to buy improved health care but do so at a cost. The chart below maps out how much we need to invest in preventive care to gain one additional quality-adjusted life year, or QALY, a standard public health measure that captures both improved longevity as well as higher quality of life:

“The evidence of hundreds of studies over the past four decades has consistently shown that most preventive interventions add more to medical spending than they save,” Russell concludes.

How can this be? The idea that prevention saves money feels intuitive. “When we think of prevention, we tend to think of the individual who benefited,” Russell writes. We conjure up an image of the woman who caught breast cancer early, averting expensive treatments, or the man who brought his weight down and lived a long, healthy life. That, however, discounts all the mammograms that didn’t detect cancer and didn’t prevent anything and all the individuals for whom weight management programs didn’t work. All those costs add up to the point that most preventive interventions cost more than they save.

If prevention doesn’t save money, one big argument in its favor gets knocked out. But that doesn’t necessarily mean there’s no reason to spend on medical interventions that make us healthier. That’s the second prong in Obama’s defense of prevention I cited earlier, that it “saves money, and it saves lives.” Slate’s Matt Yglesias pursued a similar argument this week, suggesting that the cost-saving argument isn’t always prevention’s best political defense.

Does that mean we necessarily invest in every preventive measure that takes a step towards improving health? I’m inclined to say no. Just like every treatment, preventive interventions come with their own set of risks. There’s the risk of the diagnostic test itself — increased radiation, for example, from various scans — and the possibility of an erroneous diagnosis. Some interventions, such as intensive weight loss or smoking cessation programs, also require a significant time commitment, time that presumably would be otherwise spent working, at leisure or with another pursuit. With the risks and burdens associated with prevention, it’s at least worth exploring what we gain from various interventions — how much life, as Obama puts it, gets saved.

In her chapter, Russell also runs through what $1 million invested in a given treatment buys us in Quality Life Years. Investing $1 million in screening men over 55 for colon cancer would, according to the research, translate into a gain of 577 quality life years. Investing the same amount in cholesterol-lowering medications for high-risk, middle aged men would only translate into 12 additional quality life years. Not all preventive interventions, it turns out, are created equal.

In deciding how health care gets spent, what goes to prevention and what goes to treatment, there’s no easy answer. Prevention and treatment arguably both play a role in our health-care system. Alongside Russell’s chapter in “Prevention vs. Treatment,” there are hundreds of pages of legal and philosophical arguments on how to strike the appropriate balance. Hundreds more probably could, and will, be written on how we should be best move forward in prioritizing our health-care spending.