|Standard deviation (Photo credit: Wikipedia)|
- Studies relying on large sets of aggregate data are informative in understanding group trends but tell us next to nothing about individuals. That is, the results of such a study - no matter how big or how well done - cannot reasonably be interpreted as suggesting that a particular religious person is any less intelligent than a particular atheist.
- Intelligence, as assessed by modern intelligence tests, appears to be normally distributed throughout the population. Using the mean and standard deviation from modern IQ tests (typically 100 and 15, respectively), we can calculate the portion of the population which will obtain IQ scores in various ranges. Most people (68% to be precise) will fall within 1 standard deviation of the mean (i.e., they will have IQ scores between 85 and 115). Another way to frame this would be to point out that most people are, by definition, of average intelligence.
- Very small differences become statistically significant when the sample size gets large. This is important because these some differences, while statistically significant, are too small to have much practical importance.
- Finding a negative correlation between intelligence and religiosity is certainly interesting, but is a far cry from indicating that religious belief somehow causes people to be less intelligent.