Barry Bonds and the Placebo Effect

A mathematician's guide to the news.
July 12 2001 9:00 PM

Barry Bonds and the Placebo Effect

Why Bonds won't break the homer record and the placebo effect might be bunk.

Illustration by Mark Alan Stamaty

On May 24, the New England Journal of Medicine published an article making an astonishing claim—that the power of the placebo, a core belief of medical researchers for almost 50 years, might be a statistical phantom. A few hours later, San Francisco Giants left fielder Barry Bonds came to bat against the Colorado Rockies' John Thomson and deposited a baseball into San Francisco Bay. It was Bonds' 25th home run of 2001, putting him on pace for a preternatural total of 86 for the full season. Bonds cooled after that. He went into the All-Star break with 39 home runs in his team's first 88 games, still on pace to hit 72 home runs this year and break Mark McGwire's 3-year-old record of 70 home runs in a season.

Advertisement

But Barry Bonds isn't going to hit 72 home runs for the same reason that there might be no such thing as the placebo effect. It's also the reason—according to the founder of eugenics—that humanity is doomed.

Baseball, like medicine, has more chance in it than its practitioners like to admit. There must be many reasons Barry Bonds has hit more home runs before the All-Star break than he, or anyone, ever has before. Maybe he tinkered with his stance; maybe he changed his weight-lifting regimen or took up yoga.

But one thing is almost certain: Bonds has been lucky. Is it more likely that 1) Bonds' true level of performance would have given him 30 home runs by midseason, but he caught some good breaks; or 2) that he was really hitting well enough to homer 45 times, but bad luck caused him to hit only 39? Since no one else has ever hit more than 37 home runs in a half season, the former option is the way to bet. That means we shouldn't expect Bonds to maintain his current pace; doing so would mean we were expecting Bonds to continue his run of good luck. And luck, by definition, can't be expected to persist.

Likewise, patients who are sick enough to join a clinical trial—where placebo studies are conducted—are more likely than not to be victims of bad luck. A person who's running a temperature of 104 degrees one day is relatively likely to be having a particularly bad day with respect to the fluctuations of his or her illness. On average, such people tend to have a lower fever the next day. That's true whether they take a sugar pill or not. According to the authors of the New England Journal paper, there's no strong evidence that the placebo effect amounts to any more than this. They argue that in trials where some patients are given a placebo and some are left untreated, the untreated patients don't fare measurably differently from those given the placebo. If that's so, then the placebo effect must be no more than a combination of the natural wax and wane of disease, reporting bias, and pure luck.

(That said, most researchers are not ready to chuck the placebo effect based on one article's analysis. John C. Bailar III, an editor at and former statistical consultant for the New England Journal, wrote an editorial that accompanies the placebo article in which he discusses the statistical limitations of the article's analysis, then goes on to remark, rather bravely, that with respect to the placebo effect "there is that pesky, utterly unscientific feeling that some things just ought to be true.")

What happens to the untreated patients in clinical trials, and what's going to happen to Barry Bonds, is a phenomenon called "regression to the mean," and it's been a basic principle of observational statistics ever since Francis Galton noticed in 1877 that the offspring of sweet peas tended to be closer to average size than their parents were. Galton, a first cousin of Charles Darwin and a pioneer of biostatistics, writes in his memoirs:

The following question had been much in my mind. How is it possible for a population to remain alike in its features, as a whole, during many successive generations, if the average produce of each couple resemble their parents? Their children are not alike, but vary: therefore some would be taller, some shorter than their average height; so among the issue of a gigantic couple there would be usually some children more gigantic still. Conversely as to very small couples. But from what I could thus far find, parents had issue less exceptional than themselves. (Memories of My Life, Chapter 20)

Galton's experiment with sweet peas proved that, indeed, children were on average less exceptional than their parents, for the same reason that the second half of Bonds' 2001 season is likely to be less exceptional than the first. Large parents are large partly because of their genes, partly because of luck. In the next generation, the genes are passed on, but the luck runs out.

Galton's real interest was in people, not peas. What "regression" meant to him was that the human race, if allowed to breed freely, was doomed by mathematical law to concentrate itself in the unimpressive center of the bell curve. That's why Galton is famous today not for his contributions to the science of heredity but as the creator of eugenics and the inspiration for a centurylong wrong turn in anthropology and social policy.

TODAY IN SLATE

Politics

Talking White

Black people’s disdain for “proper English” and academic achievement is a myth.

Hong Kong’s Protesters Are Ridiculously Polite. That’s What Scares Beijing So Much.

The One Fact About Ebola That Should Calm You: It Spreads Slowly

Operation Backbone

How White Boy Rick, a legendary Detroit cocaine dealer, helped the FBI uncover brazen police corruption.

A Jaw-Dropping Political Ad Aimed at Young Women, Apparently

The XX Factor
Oct. 1 2014 4:05 PM Today in GOP Outreach to Women: You Broads Like Wedding Dresses, Right?
Music

How Even an Old Hipster Can Age Gracefully

On their new albums, Leonard Cohen, Robert Plant, and Loudon Wainwright III show three ways.

How Tattoo Parlors Became the Barber Shops of Hipster Neighborhoods

This Gargantuan Wind Farm in Wyoming Would Be the Hoover Dam of the 21st Century

Moneybox
Oct. 1 2014 8:34 AM This Gargantuan Wind Farm in Wyoming Would Be the Hoover Dam of the 21st Century To undertake a massively ambitious energy project, you don’t need the government anymore.
  News & Politics
Politics
Oct. 1 2014 7:26 PM Talking White Black people’s disdain for “proper English” and academic achievement is a myth.
  Business
Moneybox
Oct. 2 2014 9:19 AM Alibaba’s Founder on Why His Company Is Killing It in China
  Life
Outward
Oct. 2 2014 9:58 AM No Word Yet From the Supreme Court on Gay Marriage 
  Double X
The XX Factor
Oct. 1 2014 5:11 PM Celebrity Feminist Identification Has Reached Peak Meaninglessness
  Slate Plus
Behind the Scenes
Oct. 1 2014 3:24 PM Revelry (and Business) at Mohonk Photos and highlights from Slate’s annual retreat.
  Arts
Brow Beat
Oct. 2 2014 10:04 AM Wearing the Button-Down Shirt of the Boy You Once Loved
  Technology
Future Tense
Oct. 1 2014 6:59 PM EU’s Next Digital Commissioner Thinks Keeping Nude Celeb Photos in the Cloud Is “Stupid”
  Health & Science
Medical Examiner
Oct. 2 2014 9:49 AM In Medicine We Trust Should we worry that so many of the doctors treating Ebola in Africa are missionaries?
  Sports
Sports Nut
Oct. 1 2014 5:19 PM Bunt-a-Palooza! How bad was the Kansas City Royals’ bunt-all-the-time strategy in the American League wild-card game?