So yesterday I posted on The Other Blog about a couple of studies purporting to find a negative correlation between religion and IQ. The short version of my conclusion is that the studies reminded me too much of white supremacist "scientists" who tried to prove the mental inferiority of African Americans in much the same fashion.
But I can almost hear someone saying, "So how would you do it, smartypants?" And it's an interesting question to answer, because, when I was going to college at the University of Nebraska at Omaha, one of the required courses for sociology majors was in research methods; one of the required projects was designing a study.
First, establishing any kind of correlation between intelligence and religiosity requires "clearing out" intervening variables that will affect the outcome, so you can compare apples to apples. The two studies in question were trying to prove that religiosity depresses intelligence. However, there may be any number of other factors that explain the apparent relationship without reaching that conclusion.
For instance, what kind of family background do religious people come from, versus the irreligious? Psychologist Paul C. Vitz, in Faith of the Fatherless, explores the relationships of several historical atheists with their fathers and finds a tendency towards fathers that were distant, absent or abusive. (It doesn't follow from that point that atheism is therefore false, I hasten to add.) Are atheists more likely to come from homes with higher incomes (and therefore more educational support)? Were their parents atheists or religiously indifferent? Are they more or less likely to have come from single-parent homes or divorced families?
Second, among the professional and academic disciplines, are there any that have a bias for or against religiosity? It would seem to be obvious that theology schools and seminaries would be biased towards religion. But what about schools of natural science and technology? Or what about the so-called "studies" (women's studies, gender studies, ethnic/racial studies, etc.) and the social sciences? What about business colleges, or the fine arts? This seems on the surface to be asking the same question as the first — intervening variables — but the problem is different. In the first case, we're asking whether any other factor affects intelligence; in this case, we're checking for a subcultural bias that pressures students towards atheism/agnosticism ... a bias that I suspect begins even with high school science textbooks.
Third, it doesn't illustrate much just to compare the median IQ scores of the religious and the irreligious. A median of 100 is the halfway point between 50 and 150, but it's also the halfway point between 80 and 120. If, I suspect, atheism is related not only to education but to subcultural bias, then it would help to compare median scores between similar levels of educational attainment. If Christian Ph.D.s have a median IQ similar to atheist Ph.D.s, then the conclusion "religion depresses intelligence" is false. Similarly, if doctorates of theology have a median within a couple of points of doctorates of physics, then the conclusion is on shaky ground. And again, if the median score of atheists is significantly higher but the distribution between the high and low is narrower, then that needs to be looked at too; it wouldn't say much if the highest scores all turned out to belong to religious people, right?
Finally, it needs to be kept in mind that, no matter which way the ball bounces, proving that one side tends to have higher IQ scores than the other doesn't prove that that side is right, or even more likely to be right. However, a couple of studies have suggested that irreligiousness is correlated with poorer physical and emotional health; one researcher even stated that irreligiousness had as negative an impact on health as a pack-a-day cigarette habit. I've already touched on some potential issues; the point of looking at physical/emotional issues is to see if there's a possible skew that's also correlated to IQ. Do parental expectations of educational achievement, for example, create an "emotional weather" that biases a person towards atheism or religiosity? Are high-IQ people more prone to alcohol or drug abuse? Is there a particular mental image of God that's more associated with irreligiousness than with religiosity, or with higher IQ than with lower IQ? Is there a left-brain or right-brain predisposition to either side?
Summing it up, then, a properly done study would ask a lot more questions and take a lot more into account in looking at a potential relationship between religiosity and intelligence. It certainly wouldn't assume that IQ scores are unmediated measures of raw intelligence; it certainly wouldn't assume that all religions had at least one god, and that to be godless was therefore to be irreligious. Above all, it wouldn't be undertaken to prove that believers are necessarily smarter or dumber than unbelievers.