This is what passes as science in 'scientific american'?! There's not a single absolute number reported aside from the laughingly small sample size of 400 adults in a world of 7,000,000,000.
This is a non-intuitive result from statistics. The standard deviation - the average expected error - does not actually depend on the population size. It could be 7 billion or 7 hundred. The standard deviation only depends on the sample size, and is O(1/sqrt(n)).
In this case, with n=400, we have O(0.05). If we are testing a random variable with two values, then the true deviation is less than 0.5, so the expected error is 0.025 - we expect no more than 2.5% of mistake. That's very good!
(The bigger question is whether the sample is random or not.)
1) zero variance in location
2) very little variance in age (all undergraduate) (variances of the ages: 1.33 to 7.19, so 70% of their samples all were in two age ranges, one 3 year wide, one 14 year wide)
3) cultural variation : essentially zero (?) they didn't even bother to check AFAICT
1: http://bleske-rechek.com/April%20Website%20Files/Bleske-Rech...