In the past, a lot of people have promoted IQ tests as if they could measure intelligence. There was a time that public schools used them to recommend careers to various people. Now, we have learned that IQ tests are measuring something, but it is not clear what exactly they are measuring! It is certainly not intelligence.
IQ tests are supposed to give the same result regardless of age or circumstance. They are also supposed to measure intelligence and only intelligence. Both of these claims are unlikely at best. IQ tests were given to poor farmers in northern India. When they had plenty of food, they scored high on these tests. When they did not have as much food, they scored low. Nor is this is only example. IQ tests have increased over time. Since other things have also increased over time such as leisure activity and health -IQ tests could be measuring one of these.
The real objection to IQ tests does not come from that source though. There are three different ways that someone could be more or less intelligent. The first way is that someone could be able to think abstractly. Since all humans and only humans can do that (leave out aliens and angels), this will not measure the difference in intelligence between any two human beings. The second way is by practice and training. Someone who has gone to school and learned how to think is better at it than someone who has not. Naturally, this does separate people into different levels of ability. But it only indicates how educated someone is. There is no reason apart from time and money that anyone cannot attain the same levels of ability as anyone else. The final way that someone could be more or less intelligent is by interest or attention. The more time and effort that you spend doing something, the better you will become at it. This is especially true when you like what you are doing. So someone who likes learning math will naturally be better at it than someone who does not like it. They will spend more time doing math and more of their attention will be focused on math.
If I am correct, and those three ways are the only ways in which people are intelligent, then IQ tests are useless. IQ tests are really measuring a combination of learning, training, attention and interest with respect to a particular kind of intellectual activity. Attention depends in part on interest and in part on competing concerns. So poor people may have little attention to spend on IQ tests. Interest is partly a matter of choice and partly a matter of nature. In either case, IQ tests are not the best instrument to find out someone’ s interest. Perhaps we could use IQ tests to measure the learning and training of someone in a particular area. However, it was not designed to do that. As it currently stands, IQ tests do not measure anything useful.