A Weblog of Centrist Voices in American Politics
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A Weblog of Centrist Voices in American Politics | |
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March 26, 2004Post hoc, ergo propter hoc"After this, therefore, because of this." Fructose Sweetener Linked to Obesity Rise If there's any one logical fallacy that pervasively permeates the public mind in regard to science, economics, politics, or almost anything else, it's the post hoc fallacy. This is the idea that just because Event B occurred after Event A, Event A is a proximate cause of Event B. And there in the morning news was a case in point, a new study that could be used to claim that special interest groups bullying subsidies out of Congress is responsible for the American obesity epidemic, simply by "doubling up" the post hoc fallacy. The reason fructose came into such massive use was that cane sugar was simply getting too expensive, due to price controls and import quotas imposed by Congress to support American sugar growers. So food and drink manufacturers switched to fructose as a sweetener, because it was cheaper. And now a group has tied the rise in the use of fructose to the obesity epidemic. So, under post hoc, we can say that political shenanigans led to fructose use which in turn led to wide-spread (snicker) obesity. We'd be utterly wrong, of course but the reasoning is appealing and it seems like an obvious and logical conclusion. But had cane sugar never been switched for fructose, we'd still be getting fatter, because we eat more than we used to, and get less exercise. And there's a nice example of the post hoc fallacy in action.... Politics indeed led to the rise in the use of fructose, but extending it to the rise in obesity is fallacious. Sadly much of what passes for politics and economics in public discussion follows this pattern. Posted by Tully at March 26, 2004 11:51 AMComments
My favorite post hoc fallacy lately is that the war in Iraq has caused the terrorists to hate us and may incite them to attack us. It's not just post hoc, it's revisionist history. Of course, terrorists have hated us for a long time and will continue to attack us regardless, unless we can stop them. Sorry, I know it's rare that we can have an intelligent discussion about society and politics without bringing up the War on Terrorism, but I couldn't resist. Posted by: Staunch Moderate at March 26, 2004 12:25 PMWell, I did say it was a pervasive fallacy! Posted by: Tully at March 26, 2004 12:49 PMresearch methods 101 Correlation is not the same as causation. This crucial logical distinction is so ingrained in myself that it's practically reflexive. And yet it seems that the failure to make this distinction just seems to grow as a quantity. I wonder what percent of it is willful and what percent flows from simple idiocy. Posted by: bk at March 26, 2004 01:41 PMBK: I would say more willful than pure stupidity. I also studied statistics in grad school and do remember that the post hoc fallacy is one of the 3 major statistical misunderstandings of the average person. One other is that group statistics do not neccessarily apply to individuals in the group. I forget the other. In all fairness thought, analysis of variance, the statistical methods used to try to sort out correlation from chance from causation is pretty tricky and fraught with error, even by researchers. Posted by: tallan at March 26, 2004 03:52 PMIgnorance of base assumptions (asssumed relevance). If you don't know how the data was generated and the base assumptions used to interpret them and design the study, you actually have no idea at all what the statistics mean. There are some less obvious errors that are just as bad. False rejection of the null hypothesis. The idea that the size of an effect is indicative of its importance. And so on. Posted by: Tully at March 26, 2004 05:38 PM |
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