Tuesday, March 26, 2013

Texas Sharpshooter: Adventures in Logic III

Dear Children:

This may be new to you, but bear with me. You will be rewarded.

Correlation does not imply causation (cum hoc propter hoc). That is Latin for "with this, because of this". It is a term used in science and statistics to emphasize that a correlation between two variables does not necessarily imply that one causes the other. Many statistical tests calculate correlation between variables. A few go further and calculate the likelihood of a true causal relationship.

The opposite assumption, that correlation proves causation, is one of several logical fallacies by which two events that occur together are taken to have a cause-and-effect relationship. This fallacy is also known as cum hoc ergo propter hoc, Latin for "with this, therefore because of this", and "false cause". A similar fallacy, that an event that follows another was necessarily a consequence of the first event, is sometimes described as post hoc ergo propter hoc (Latin for "after this, therefore because of this").

You only have to remember the gist: one thing does not cause the other because they occur near, before or after the other thing.

One interesting version of this is in the news every day; the medical news. It’s called The Texas Sharpshooter fallacy. Sorry, there is no Latin word for Texas.

This fallacy posits that if there are at least two factors that present themselves in a large sampling of data, the same conclusion may be drawn as from the whole sample. It’s as if someone shot a million .45 rounds in the broad side of a barn. After examination of the bullet holes, our gunman draws a target around two of them claiming a medal for marksmanship.

It would be funny if it didn’t have tragic consequences. Our brains are wired to look for patterns. That’s how we recognize faces for instance.

Thousands of parents have refused to have their children vaccinated because of this cruel fallacy. A child has autism, that child got vaccinated; vaccination causes autism. It’s not as if parents were making a tragic mistake for their own children but they are also risking exposure to Rubella, for instance, to their children’s classmates. Remind me to talk about Moral Hazard some day.

Not that there aren’t hilarious examples of this as well, Sports radio is full of it. Some talking head notices that Bruiser’s ERA seems to fluctuate with his picture on the first page of the sports section of the paper. That’s fun but no less a load of equines puckes.

I’m just sayin’


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