What's a Few IQ Points Between Sisters?

Just because you can measure that something is different doesn't necessarily mean that you've learned anything meaningful. That's my take on the latest study that purports to show that, as a group, first-born children tend to have a slightly higher IQ or intelligence quotient than their younger siblings. The IQ difference, reported in the research journal Science, was only 2.3 points (where 100 points is the average) in a study of male Norwegian military recruits.

The decision by the editors of the New York Times to showcase Benedict Carey's reporting about the Norwegian IQ study on the newspaper's front page guaranteed that the report would get picked up by many other news venues and bloggers--me included.

Let's take the study at face value for a moment and assume that there's nothing wrong with the methodology or conclusions. Such a modest difference may be statistically significant--meaning that the possibility that this result is due to random chance is low--but that doesn't necessarily mean it makes a difference to individuals or even society at large. Can you really tell the difference between someone with an IQ of 100 or 103? 120 or 123?

Furthermore, even if true, a slightly higher IQ doesn't necessarily mean that firstborns will excel in business, succeed in starting their own company, create great music or advocate for social change. Nor will a slightly higher IQ necessarily protect them against racism, sexism or the heartbreak of psoriasis.

Science is full of examples of finding differences that turned out to be unimportant. Taking estrogen for years after menopause increases an older woman's good cholesterol levels and lowers her bad ones. Turns out, as the Women's Health Initiative Study showed, that does not to make one bit of difference in whether she'll have a heart attack--in fact, in some cases, it actually increases her risk slightly.

So, I don't set much store in the Norwegian IQ study--even though I am a firstborn myself. The history of IQ studies is so flawed, the purported difference is so slight, that it just doesn't mean much to the real world in which most of us live.

Source: Kristensen and Bjerkedal. "Explaining the Relation Between Birth Order and Intelligence." Science 22 June 2007: Vol. 316. no. 5832, p. 1717