4. There are very few measures I’ve ever found that satisfied both conveying useful and understandable information quickly. NNT might just be it.
As statistical tools go, the idea of the number needed to treat is relatively new. It was first described in 1988 by epidemiologists Andreas Laupacis, David Sackett, and Robin Roberts in a New England Journal of Medicine article titled “An Assessment of Clinically Useful Measures of the Consequences of Treatment.” They start by sketching out the problems with a number called the relative risk reduction. That’s the measure you often see hyped in media reports of scientific studies. Imagine, for example, a study of heart disease that finds that a new drug reduces the risk of death by an astonishing 50 percent. The reality behind that number is that the risk of death over a 10-year period for, say, a healthy 45-year-old man weighing 200 pounds went from 5 percent to 2.5 percent—50 percent! Such a finding is clinically significant, yes. Worthy of publication, maybe. But not quite as astonishing.
It would be better, the authors write, to look at a number called the absolute risk reduction—the 2.5 percent reduction that resulted from the new drug. But working with that measure can be hard to understand, because it is actually a percent of a percent. To make it more intuitive and apprehendable, the authors explain, you can use the inverse of absolute risk reduction: Divide 1 by 2.5 percent, or .025, to get 40. And that’s the number needed to treat. Forty people have to take the drug for one person to benefit. So is it worth taking? That depends. The NNT isn’t crazy high, so you might go for it, especially since a heart attack can kill you. But if the drug has terrible side effects, you might not. “Different people value different things differently,” Laupacis says. “So they might be more scared of the rare harm.” On the other hand, when the original article on AZT came out in the early days of the AIDS epidemic, the NNT to prevent one death was around 6 (that’s very good). “It can also tell you to do something,” he says.
5. This map of languages looks exactly as though it belongs in the appendix of a fantasy novel.
6. Does Depo-Provera (the contraceptive shot) increase HIV transmission? And why haven’t we tried to find out? (Answer, because it’s complicated and even if it does, would taking away that option in Sub-Saharan Africa increase total deaths?) (h/t Ed Yong)
Every study that has linked Depo-Provera — or DMPA, as researchers call it — to HIV infection has been observational. So although a well-regarded DMPA study estimates that the contraceptive might double a woman’s risk of acquiring HIV, policy-makers and charitable organizations that provide countries with contraceptives have yet to change their policy on Depo-Provera. That’s where the new trial comes in; it could provide confirmation of the observational results — or show that they weren’t reliable.
The proposed trial has its share of critics, though. Some think it would unethical to ask women to take DMPA for an extended period, because it would amount to knowingly putting them in harm’s way; these critics think the observational data already supports an immediate phasing out of DMPA. Others think a trial shouldn’t lead to a global ban on DMPA, even if results show that the drug has increased the rate of HIV infections. In most countries, removing it would ultimately cause more deaths than leaving it be, some experts say, because a greater number of women would end up dying during childbirth without it.
8. I have so little interaction with babies or people with babies (a recent conversation with friends had me drawing the conclusion that it’s been about five years since I was anywhere near someone under the age of eight), that I’ve been especially enjoying Julia’s pieces on childcare and breastfeeding.
Things I read this week:
–The Trial of Henry Kissinger, Christopher Hitchens
Good, but hard to follow if you don’t have a firm grasp of history from that time period.
–Wild, Cheryl Strayed
Memoir, not really my style, but worth finishing at least
–Rhapsody (Symphony of Ages, Book 1), Elizabeth Haydon
Science fiction with character development and no obvious ‘bads’ or ‘goods’. Yes, I heartily approve.
–Americanah, Chimamandah Ngozi Adichie
I’m just not really a ‘people in the modern era living complicated lives’ novel reader. I like mystery or sci-fi or historical fiction or at least a dusting of intrigue. And all of that being true, I loved this book.