Judith Rich Harris, correlation, and causation
In 2001 Judith Rich Harris published “The Nurture Assumption”, which, from the many favourable mentions I’ve seen in a variety of contexts, seems to have had a considerable influence on our thinking about how human beings develop.
I haven’t yet been able to get a hold of Harris’ book, but I did just find an essay by her in a collection of essays put together by John Brockman, “The Next 50 Years”.
The argument Harris makes in the essay can be summarized as follows:
(a) Genetic factors play a large (though far from exclusive) role in controlling human development.
(b) Most studies in developmental psychology assume that it is the environment that determines human behaviour.
(c) Those studies therefore fail to control for genetic effects.
(d) Those studies are therefore essentially useless.
It’s a fascinating argument: simple, yet if correct, devastating for an entire academic field.
(To avoid any confusion in attribution, I should say that I don’t know who originated this argument, although it is clear that Harris is but one of many contributors.)
Everyone knows, at some level, that correlation does not imply causation, but it is difficult to avoid the fallacies that can result when one is not mindful of this.
It occurred to me when talking with my partner, Jen, this evening that I don’t have a nice vivid example of this point ready at hand. So we made one up that I think illustrates the point memorably.
Suppose one observes top basketball players, and notices that they all tend to wear very expensive basketball shoes. Is one justified in assuming that more expensive basketball shoes cause someone to be a better basketball player?
In some small measure, the answer is yes. But it doesn’t matter what you put on my feet, I’m never going to jump like Michael Jordan.
Indeed, marketing in general seems to be based largely on the fact that, at some level, in many cases subconscious, we easily confuse correlation with causation.