Average IQ scores declined by six points. However, children aged between five and 10 saw their IQs increase by up to half a point a year over the three decades.

What causes IQ to drop?

Micronutrients and vitamin deficiencies. Micronutrient deficiencies (e.g. in iodine and iron) influence the development of intelligence and remain a problem in the developing world. For example, iodine deficiency causes a fall, on average, of 12 IQ points.

What percent of the population has an IQ score greater than 100?

IQ tests are made to have an average score of 100. Psychologists revise the test every few years in order to maintain 100 as the average. Most people (about 68 percent) have an IQ between 85 and 115. Only a small fraction of people have a very low IQ (below 70) or a very high IQ (above 130).