Question: What are sisters good for?

Answer: increasing your score on a 13-question test of happiness by 1 unit on one of the 13 questions.

A recent study of the effect of sisters on happiness has been getting a lot of press since it was featured on at the New York Times. It's just started hitting my corner of the blogosphere, since Mark Liberman filing an entry at Language Log early in the evening. On the whole, he was unimpressed. The paper didn't report data in sufficient detail to really get a sense of what was going on, so he tried to extrapolate based on what was in fact reported. His best estimate was that having a sister accounted for 0.4% of the variance in people's happiness.

This is a long way from the statement that "Adolescents with sisters feel less lonely, unloved, guilty, self-conscious and fearful", which is how ABC News characterized the study's findings, or "Statistical analyses showed that having a sister protected adolescents form feeling lonely, unloved, guilty, self-conscious and fearful", which is what the BUY press release said ... Such statements are true if you take "A's are X-er than B's" to mean simply that a statistical analysis showed that the mean value of a sample of X's was higher than the mean value of a sample of Y's, by an amount that was unlikely to be the result of sampling error.

Only an hour later, the ever wide-eyed Jonah Lehrer wrote

There's a surprisingly robust literature on the emotional benefits of having sisters. It turns out that having at least one female sibling makes us happier and less prone to depression...

I think this demonstrates nicely the added value of blogging, particularly science blogging. Journalists (like Lehrer) are rarely in a position to pick apart the methods of a study, whereas scientist bloggers can. I know many people miss the old media world, but the new one is exciting.

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For more thoughts on science blogging, check this and this.