Intelligence tests were invented in 1904 by Dr Alfred Binet, in response to a request of the French minister of education for a way of distinguishing the gifted, normal and challenged children in the school system so that the education that they received could be delivered at the right level. What he came up with was a test that delivered a number that could be used to rank individuals according to their assumed intelligence. This is called the Intelligence Quotient, or IQ for short.
Ever since, they have been used for assorted inappropriate purposes, some of which were discriminatory, and most of which were totally outside the design and usage requirements of the test. Because of this there are now some laws in parts of Europe that will enable you as an employer to be prosecuted if you use them prejudicially.
Problems with Intelligence Tests
As these tests became more widespread, other problems were found with them. One was that the tests only work properly for the "normal" population. For people at the more extreme ends of the intelligence range, you must use specially calibrated tests which are harder to calibrate due to the much smaller sample size.
Another problem has to do with test bias. These can range from alternative answers, to cultural bias like assuming that everyone has read "the classics". This is dealt with by cross indexing the questions, and every time you find a set of answers that vary significantly from the normal, you ask the person who took the test why his answer was different. You then have to modify the test to remove this identified source of error.
Every time you modify the tests you must then re calibrate the test.
The alternate answers problem stems from asking open questions, without realizing that you are doing it. This is dealt with by working hard to detect them.
General or Specific Intelligences
After a while, it began to be found that some of these error causing questions all pushed in the same direction, and the idea of specific intelligences began to emerge. This lead to the ordinary test being optimized to give your general intelligence which is independent of these specific types, and various other tests being developed to measure the specific types separately.
Part of the Intelligence Project