Correlation: Joy of Stats

[multiple speakers]

[the video shows a man riding on a boat on a lake. His name is Professor Hans Rosling:]

Professor Hans Rosling: I got a joke about silly correlations. There was this American who was afraid of heart attack, and he found out that the Japanese ate very little fat and almost didn’t drink wine, but they had much less heart attacks than the American. But on the other hand, he also found out that the French eat as much fat as the Americans and they drink much more wine, but they also have less heart attacks. So he concluded that what kills you is speaking English.

[another man is shown on screen, named Sir Michael Marmot]

Sir Michael Marmot: The standard criticism of correlations is that correlation is not causation. It’s often used as a cheap shot “oh that’s just a correlation”, “they’re just statistics, you haven’t proved anything”.

[the video then shows an old advertisement for cigarettes,]

Advertisement: Smoke, smoke, smoke that cigarette! Puff, puff, puff it if you smoke yourself to death!

[another cigarette commercial is shown]

Advertisement2: The time, the pace, the cigarette, weights tilt!

Professor Rosling: The best example of a really groundbreaking correlation is the link that was established in the 1950s between smoking and lung cancer. Not long after the second world war, a British doctor, Richard Dahl, investigated lung cancer patients in twenty London hospitals, and he became certain that the only thing they had in common was smoking. So certain that he stopped smoking himself, but other people weren’t so sure.

[the video shows Sir Marmot again]

Sir Marmot: A lot of the discussion of the early data linking smoking to lung cancer said “was not the smoking, surely that thing that we’ve done all our lives, that can’t be bad for you, maybe it’s genes, maybe people who are genetically predisposed to get lung cancer are also genetically predisposed to smoke”. Maybe it’s not the smoking, maybe it’s air pollution, that smokers are somehow more exposed to air pollution than non-smokers. Maybe it’s not smoking, maybe it’s poverty. So now we’ve got three alternate explanations apart from chance.

[the video shows more advertisements for cigarettes, and the production of cigarettes.]

Professor Rosling: To verify his correlation did imply cause and effect, Richard Dahl created the biggest statistical study of smoking yet. He began tracking the lives of forty thousand British doctors, some of whom smoked, and some of whom didn’t, and gathered enough data to correlate the amount the doctor smoked with their likelihood of getting cancer. Eventually, he not only showed a correlation between smoking and lung cancer, but also a correlation between stopping smoking and reducing the risk. This was science at its best.

Sir Marmot: What correlations do not replace is human thought. You could think about what it means. I mean what a good scientist does, if he comes up with a correlation, is, try as hard as she or he possibly can to disprove it, to break it down, to get rid of it, to try and refute it. And if it withstands all those efforts at demolishing it, and it’s still standing up, then cautiously you say we really might have something here.

[another commercial is shown for cigarettes]

Advertisement3: Tell Saint Peter at the Golden Gates that you hates to make him wait, but you just gotta have another cigarette!

Professor Rosling: To find out more about the joy of stats, visit the Open University’s open learn website.

[end of video]