"Nigel, who has an IQ of 180, is also a maths whiz.." - The AgeThis got me thinking. What does it mean to have a 180 IQ. IQ is a norm score. IQ typically has a mean of 100 and a standard deviation of 15. Thus, I asked the following questions:
- What's the probability of having an IQ of 180 or higher?
- One in how many people would have an IQ 180 or higher?
- What's is the probability that someone who a newspaper reports as having a 180 IQ or higher, actually has an IQ of 180 or higher?
I decided to do some armchair stats in R:
iqValues = seq(100, 180, 5);
pThisIqOrHigher = 1 - pnorm(iqValues, mean = 100, sd = 15);
oneInThisMany = 1 / pThisIqOrHigher;
pThisIqOrHigherFormatted = formatC(pThisIqOrHigher,
digits = 8, format = "f");
oneInThisManyFormatted = formatC(oneInThisMany,
digits = 0, width = 10, format = "f");
cbind(IQ=iqValues, p=pThisIqOrHigherFormatted,
OneIn=oneInThisManyFormatted)
# IQ p OneIn
# [1,] "100" "0.50000000" " 2"
# [2,] "105" "0.36944134" " 3"
# [3,] "110" "0.25249254" " 4"
# [4,] "115" "0.15865525" " 6"
# [5,] "120" "0.09121122" " 11"
# [6,] "125" "0.04779035" " 21"
# [7,] "130" "0.02275013" " 44"
# [8,] "135" "0.00981533" " 102"
# [9,] "140" "0.00383038" " 261"
# [10,] "145" "0.00134990" " 741"
# [11,] "150" "0.00042906" " 2331"
# [12,] "155" "0.00012287" " 8139"
# [13,] "160" "0.00003167" " 31574"
# [14,] "165" "0.00000734" " 136176"
# [15,] "170" "0.00000153" " 653327"
# [16,] "175" "0.00000029" " 3488556"
# [17,] "180" "0.00000005" " 20741279"
- The probability of having an IQ of 180 or higher is 0.00000005.
- That's one in about 20 million. I.e., if the norm sample was Australia, he's either the smartest or one of the top few smartest people in Australia
- As for my thoughts on the final question: I think it's pretty low.