Hi It was me who wrote that caption however I did not say originally My sentence is The IQs of a large enough population are calculated so that they conform to a normal distribution I totally agree with you that this is not how it was done originally but as far as I know this is how it is done today Unfortunately I don t have a specific source for it but it is basically what I have understood from reading lots of intelligence test manuals books on assessment and intelligence etc There is no research that says that amount of intelligence is distributed across the population in the same way as a normal distribution but this is the way IQ tests are made For example if a small country suddenly gets a high influx of highly intelligent immigrants suddenly more than 50 of the population would have an IQ of 100 or higher But instead of changing the normal distribution the next time when they standardize the IQ test they take a representative sample of 1000 or 10 000 inhabitants and the ones that have an average intelligence get IQ 100 the 2 most intelligent people get IQ 130 or more the 2 least intelligent people get IQ 70 or less This is how I have understood the statistics behind IQ However I am not a statistics specialist at all so please correct me if I am wrong talk