Mammograms Revisited

Richard Thaler (coauthor of Nudge; I'll reference him often) wrote a piece for the NY Times about the current mammogram controversy. It's worth a read. He doesn't talk about "saving lives", he brings up the problems with prostate cancer treatment, and he provides some interesting numbers about the likelihood that breast cancer is not fatal and mammograms don't detect the types that are fatal, though not the expected life spans of women who are treated for breast cancer. I have a little commentary to add.

The stated false positive rate is 10% per test (which is huge for something with such serious consequences). For the math impaired, here's how that converts into the probability that women are likely to get a false positive over a decade. The simplest way to do this is to focus on the 90% chance that each test does not give a false positive. We use what is called the Multiplication Rule for Independent Events. For ten years, we multiply .9 (90%) by itself nine times: .9 * .9 * .9 * .9 * .9 * .9 * .9 * .9 * .9 * .9. This is more simply written as .9 ^ 10, and the product is about .35. So, there is a 35% over ten mammograms that a woman will not get a false positive, and a 65% chance that she will get a false positive. Of course, this assumes that there are no characteristics of a breast that would make it prone to false positives, which I imagine is unlikely. The 10% comes from aggregate data. I think it is more probable that women who produce false positives at age 40 are continuously more likely to do so each year than women who did not have false positives at age 40. Without the longitudinal data in front of me, I remain skeptical of the appropriateness of multiplying the false positive probabilities as though they are always independent events.

Thaler writes a little about the costs of all these mammograms in terms of unnecessary treatments that cause side effects, and the stress that women feel when diagnosed with breast cancer, but he avoids using dollar amounts to describe all the waste. What is missing is mention of opportunity costs. The cost of all the unnecessary procedures is not just the dollars exchanged for them, but also the other things we can not buy because our finite dollars were poorly allocated. I covered in my last post the idea that we could extend several times as many life years for Americans by taking the money spent on mammograms for women under 50 and spending on other endeavors, such as nutrition programs for children, or having nurses visit patients after operations to reduce treatment noncompliance complications. It is vital to consider opportunity costs. Mammograms for women under 50 don't just allocate $2 billion per year in exchange for a few thousand life years. They also cost us many thousands of other people's potential life years, and the unnecessary treatments and stress result in much lost work productivity. The practical net result, the way I see it, is that our system is effectively just killing other people early by insisting on giving mammograms to women under 50 who lack high risk indicators. Are women in their 40s more important than everyone else?

Many people have lost or almost lost loved ones to breast cancer. It is okay to feel empathy for them. If you are one of them, I feel empathy for you. That is not justification to ignore the data we have and allocate our limited resources on inferior practices. Emotions limit our perspectives and distract us from the ultimate goal of doing the most good we can with the resources we have. Please, let the cooler minds prevail and establish a system that gives America the greatest benefits it possibly can.

Mammograms

The current mammogram controversy is yet another example of ignorant, unthinking people going crazy about something they don't understand. Most critics of the new U.S. Preventive Services Task Force guideline do not understand that our system has finite resources. They also don't understand that there is no such thing as saving a life. There is only delaying death. Also not mentioned in any of the articles I am reading is that breast cancer mortality rates are usually only measured for five years.

The new guideline says that the recommendation for mammograms should be once every two years starting at age 50. This replaces the recommendation for annual mammograms starting at 40. They found that only 1 in 1900 mammograms for women in their 40s delayed death. This may save $2 billion per year and result in maybe 600 undelayed deaths. That means the old guideline resulted in spending about $3.3 million dollars per delayed death. I don't know the life expectancy of breast cancer survivors, but for the sake of more math, let's say that all of these deaths were delayed by 40 years. That's over $83,000 dollars per year of life, just spent on mammograms! Keep in mind that these women will continue to incur more health care costs over those 40 hypothetical years, too, and I am not considering quality of life.

The British system refuses to pay for drugs that cost more than $45,000 per quality-adjusted life year (QALY). Medicare limits hospice spending to about $22,000 per year (if I read that right). These measures are necessary to protect the whole system from going bankrupt, as our system is destined to by 2017 unless we make drastic changes. These measures also help ensure that the system's finite resources are being used where they can do the most good.

Think about how much good could be done with that $2 billion per year. I guarantee that we could save far more than the breast cancer's 24,000 (my certainly too-high hypothetical estimation) life-years by spending it somewhere else. I bet that $2 billion could be easily spent to save 100,000 life-years or more. Critics of the new guidelines are selfish and short-sighted, and would rather hang on to their anecdotes of women whose deaths were delayed while sentencing thousands of other people to a lack of care due to insufficient resources. These costs also keep insurance premiums high, pricing working poor out of comprehensive insurance.

Women considered high risk due would still be recommended for mammograms before 50. There is some talk about how black women would be disadvantaged by the new guideline because they tend to have earlier and more aggressive cancers, and of course that would be taken into account by informed doctors making recommendations. The task force guideline is based on aggregate information for the national population.

Mammograms have been oversold, and our country as a whole would be better off following the new guidelines. We need to make our entire system more efficient and cost effective (not the same as cutting the total cost, just demanding better results for our money) for it to be sustainable and good for the people of our country.