The Target group was 70 children aged between five and 14, described as gifted by their parents, almost entirely without testing, all of whom had joined the National Association for Gifted Children. Each Target child was matched with two Control children
Of the whole sample, 170 children were at the 99th percentile of the Raven�s Matrices. Stanford-Binet IQs ranged from the 46 children with less than IQ120 to 18 children with above IQ160; 13 reached the Stanford-Binet test ceiling of 170 IQ.
Okay, I totally, completely do not understand these numbers. Maybe someone else can help.
Her data was collected in 1974, when the population of the UK was around 56 million. Of that number, probably around 11 million were kids under 18 (basing this on current numbers of 14.1 million 20 and under and making an estimate).
An IQ of 170 on an SB occurs once in
652,600 people. So finding 13 kids with that IQ means she enrolled more than 75% of this total population from all over the UK.
Really? Wow. Are there any other people here who've identified
and consented 75% of a national population of people with some very rare and non-obvious characteristic? If so, please tell me your secret. See arithmetic at end.
Yet I think her sample size was only 210, so she should have been surprised to find even one kid with an IQ of
145, let alone 170, even among a self-selected high IQ group.
More confusing is that she only had 46 people with IQs under 120. This is only 22% of her total population, yet an IQ of at least 120 occurs in 1 out of every 11 people. At a minimum, nearly everyone in her random-kids group (70 kids, right?) should have had an IQ below 120, yet even if all 46 were in the non-gifted group, they'd only comprise about 2/3 of it.
Bottom line: this data smells to me. It's puzzling why the reviewers didn't pick this up.
Maths:
13*652,600 = ~8.5 million
8.5 million/11 million = 0.77
0.77 * 100 = 77%
