Monday, October 5, 2009

Causation and Responsibility

Any good scientists knows that correlation is not causality, and any good science writer mentions this fact as often as possible, as I did recently.

But there is another very important point that is not mentioned enough.  I've never actually seen anyone state it in simple terms:

Causation is not Responsibility.

See if you can tell the difference between following two statements:

1) Abortion laws have been shown to have a statistically significant effect on rates of violent crime.
2) Legalizing abortion is responsible for the recent drop in violent crime.

The first statement is true, and the second is not, even though journalists often translate the first into the second.

The problem lies not with the actual words used, but with their connotation.  A lot of people have the idea that only one thing is responsible for most effects.  The human brain seems hard-wired to think in terms of simple narrative causality, and our legal system reinforces this notion.  But reality is messy and complicated, and there are usually a lot of reasons for things to happen.  There may be five or six causes that all work together to produce an effect, and the way that the causes interact can get very complicated.

Often, different scientific studies will show that different things cause the same effect.  For example, there are papers showing that different policing methods cause a drop in crime. Sometimes this leads to a dispute.  But it usually turns out that both papers are true.  One thing explains part of the variation, and another thing also explains part of the variation.  Knowing that one thing causes something does not imply that other things have no effect.

It is especially important to remember this fact when reading about the effect that genes have on life outcomes.  Yes, it is true that genes cause things.  You can make reliable predictions about peoples' life outcomes by looking at their genes.  But genes are not solely responsible; they may only explain a quarter of the variation.  The other three-quarters is environmental.  So no matter what your genes say, the choices you make and the situations you put yourself into will still be responsible for most of your fate.

Genes can often make your life harder, forcing you to work a lot to accomplish something, like a good body or social skills, that come naturally to other people.  But the fact that you have the gene that causes something like alcoholism or obesity does not change the fact that you are the one responsible or your life.

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