美国国家公共电台 NPR Researchers Show Parachutes Don't Work, But There's A Catch（在线收听）

SCOTT SIMON, HOST:

This just in - research published in a major medical journal concludes that a parachute is no more effective than an empty backpack. But before you leap to any conclusions, hear the whole story from NPR science correspondent Richard Harris.

RICHARD HARRIS, BYLINE: The gold standard for medical research is a study that randomly assigns volunteers to try an intervention or to be in a control group. For some reason, nobody has ever done a randomized controlled trial of parachutes. In fact, medical researchers often use the parachute example when they argue they don't need to do a study because they're so sure they already know the answer. Dr. Robert Yeh at Harvard Medical School got a wicked idea one day. He and his colleagues would actually attempt the parachute study to make a few choice points about the potential pitfalls of research. They started by talking to their seatmates in airliners.

ROBERT YEH: We'd strike up a conversation and say, you know, would you be willing to be randomized in a study where you had a 50 percent chance of jumping out of this airplane with versus without a parachute?

HARRIS: Did you get any takers?

YEH: (Laughter) For the most part, we did not on those commercial airlines.

HARRIS: And those who said yes were excluded for reasons of questionable mental health. They had much better success asking members of their own research teams, from Harvard, UCLA and the University of Michigan, about volunteering to participate in the experiment on other aircraft.

YEH: Either a small biplane - that was our group that - we went to Martha's Vineyard and did that, and the group in Michigan went and jumped out of a small helicopter in fact.

HARRIS: The 23 people who agreed to jump from the smaller aircraft represented quite a skewed sample, which was part of the point Yeh and his team were trying to make. Photos taken during the experiment show the volunteers were only too happy to take part.

YEH: I think people are for the most part laughing all the way down to the ground.

HARRIS: Right, which is about two feet or something.

YEH: Exactly right (laughter).

HARRIS: Oh, a minor detail here. The biplane and helicopter were parked, so it's not surprising that nobody suffered any injuries. It's literally true that parachutes offered no better protection for these jumpers than the backpacks.

YEH: And, of course, the top line of results would be that parachutes don't work. But, of course, that is a ludicrous result. The real answer is that that trial did not show a benefit because of the types of patients that were enrolled.

HARRIS: If they had enrolled people at high risk for injury - that is, people up in the sky - the results would have been quite different, not to mention unethical. Their study is published in the traditionally lighthearted Christmas issue of the medical journal BMJ.

YEH: It's a little bit of a parable to say that we have to look at the fine print. We have to understand the context in which research is designed and conducted to really properly interpret the results.

HARRIS: Emory University epidemiology professor Cecile Janssens says via Skype this is a real problem in science.

CECILE JANSSENS: I know that people often don't look detailed enough into what is being investigated to know how they can interpret the results of a trial.

HARRIS: Janssens was delighted to come across the paper on Twitter. She says, like a lot of research, the results are accurate as far as they go.

JANSSENS: Results of this trial can only be generalized to situations where people jump out of an aircraft that's within a few feet above the ground.

HARRIS: She plans to give this paper to her students with a straight face and see how long it takes for them to get the deeper points about scientific methodology buried in this absurd experiment.

JANSSENS: It'll be unforgettable.

HARRIS: Yeh is pleased to see that the fun he has had with his colleagues is turning into a teaching tool.

YEH: And our greatest, I think, accomplishment from all of this is that we felt very good that we were able to cite Sir Isaac Newton in the paper.

HARRIS: Yes, I noticed that. It was in fact his original publication from - what was it? - 1687.

YEH: (Laughter) That's right.

HARRIS: Yes, gravity is a law. Mess with it at your own risk. Richard Harris, NPR News.