From Wikipedia's page on Mental age, we learn that:Originally, the differences between mental age and chronological age were used to compute the intelligence quotient, or IQ. This was computed using the ratio method, with the following formula: mental age/chronological age * 100 = IQ. No matter what the child's chronological age, if the mental age is the same as the chronological age, then the IQ will equal 100.[4]  An IQ of 100 thus indicates a child of average intellectual development. For a gifted child, the mental age is above the chronological age, and the IQ is higher than 140; for a mentally retarded child, the mental age is below the chronological age, and the IQ is below 70.In this way, precocious children can get exceptionally high scores (e.g. scores above 160, s.d. 15), even if they answer correctly only a fraction of the total number of questions, provided the test is sufficiently hard in comparison with their actual chronological age. However, I am not aware of any tests for adults that discriminate accurately above the threshold of IQ $\sim$ 160 - their accuracy is even less than 4 s.d., taking into account a ceiling effect. How can psychometry assess an IQ of 170 or 180 in adults when the rarity of such scores is 1 in several millions?Can the IQ scores of exceptionally and profoundly gifted children be extrapolated into adulthood?Is it true that that a profoundly gifted child with an IQ of 170 would score better than 99.9998% of the general population?It seems that two different definitions of IQs are used here: is there a correlation between them?
How can psychometry measure the very high IQ's in adults?
intelligence