Analysis / Improbably Low IQ

To illustrate exactly how improbable a given IQ score might be, see the following table of statistics on below average IQs. Scores are from the Stanford-Binet test, the original and best-known IQ test — see here. They follow a normal (bell curve) distribution with a mean of 100 points and a standard deviation of 15 points.

IQ Occurrence Frequency On Earth (of 7 500 000 000)
≤10050% 1 in              2 3 750 000 000
≤ 9537% 1 in              3 2 770 810 051
≤ 9025% 1 in              4 1 893 694 032
≤ 8516% 1 in              6 1 189 914 404
≤ 8009.1% 1 in             11 684 084 148
≤ 7504.8% 1 in             21 358 427 642
≤ 7002.3% 1 in             44 170 625 990
≤ 6500.98% 1 in            102 73 614 965
≤ 6000.38% 1 in            261 28 727 854
≤ 5500.13% 1 in            741 10 124 235
≤ 5000.043% 1 in          2 331 3 217 952
≤ 4500.012% 1 in          8 139 921 498
≤ 4000.003 2% 1 in         31 574 237 534
≤ 3500.000 73% 1 in        136 176 55 076
≤ 3000.000 15% 1 in        653 327 11 480
≤ 2500.000 029% 1 in      3 488 556 2 150
≤ 2000.000 004 8% 1 in     20 741 279 362
≤ 1500.000 000 73% 1 in    137 360 560 55
≤ 1000.000 000 099% 1 in  1 013 594 692 7
≤  500.000 000 012% 1 in  8 336 096 322 1
≤  000.000 000 001 3% 1 in 76 429 666 480 0
http://tvtropes.org/pmwiki/pmwiki.php/Analysis/ImprobablyLowIQ