Correlation vs. Causality: Freakonomics Movie [MUSIC PLAYING] MAN: Freakonomics, Freakonomics. CAPTAIN KANGAROO (ON TELEVISION): Well hi there boys and girls. This is Captain Kangaroo. Say, I'd like you to meet a friend of mine. So you know it's lots and lots of fun to have a pet that you can run and play and jump with, isn't it? But did you know that there are some boys and girls who can't run and jump and play? It's all because of a thing called polio. - When I think of bad historical assumptions about correlation and causality I think of polio a hundred years ago when it was this horrible mystery that it was claiming a lot of lives and it was really scary because it mostly struck children. And there was a strong line of research that suggested that ice cream caused polio, that ice cream consumption caused polio. GIRL: Here comes Mr. Softee, the soft ice cream man. ALL (SINGING): The creamiest, creamiest soft ice cream you get from Mr. Softee. - The reason that that correlation was thought to be causal was that polio spiked in the summertime, for reasons that really weren't very well understood, but it did. And ice cream sales spiked during the summertime. So these researchers had seen that whenever there was a lot of ice cream being sold and consumed there was a lot more polio. And so there was really literally the beginnings of this kind of ice cream persecution to try to stomp out polio. And it sounds ridiculous, but you see it all the time now of people trying to fight against or build up something that they're sure is connected to something else and which it turns out just isn't.