Normal CurveNearly all comparisons concerning intelligence are based on the assumptions of the Normal Curve.
Test scores can be converted to Percentiles using means and standard deviations.
34.13% of individuals fall one standard deviation above and below the mean, resulting in 68.26% falling within 1 standard deviation:
13.8% of individuals fall between one and two standard deviations above and below the mean, resulting in 95.44% falling within 2 standard deviation:
2.1% of individuals fall between two and three standard deviation above and below the mean, resulting in 99.72% falling within 3 standard deviation:
Only .1% of individuals fall greater than three standard deviations above and below the mean...
So, a bit of knowledge about one's score on a standardized test (ie, score, mean, standard deviation) can reveal more than one might like: