An intelligence quotient (IQ) is a total score derived from one of several standardized tests designed to assess human intelligence. The abbreviation “IQ” was coined by the psychologist William Stern for the German term Intelligenzquotient, his term for a scoring method for intelligence tests he advocated in a 1912 book.
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The average IQ has to be 100 by definition, but the percentage of questions answered correctly is an arbitrary number that depends on how hard the questions are.
In 1980’s the test mongers had to map the percentage-correct scale onto the IQ scale by a formula. The average scores on the tests had been creeping up for decades, so to keep the average at 100, every once in a while they jiggered the formula so the test takers would need a larger number of correct answers to earn a given IQ. Otherwise there would be IQ inflation.
Later generations given the same set of questions as earlier ones, got more of them correct. Later generations must be getting better at whatever skills IQ tests measure.
An average teenager today, if he or she could time travel back to 1950, would have had an IQ of 118. If the teenager went back to 1912, he or she would have am IQ of 130, besting 98% of his or her contemporary.
If typical person of year 1910, time-transported forward to present, would have mean IQ of 70, which is at the border of mental retardedness.
The biggest gains in IQ test is in the items that do not tap knowledge, vocabulary or arithmetic. They are found in the items that tap abstract reasoning(‘What do a pound and an inch have in common?’), analogies(‘BIRD as to EGG as TREE is to what?’) and visual matrices.
Thinking Beyond Science 
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