The problem with Galton’s approach was an utter lack of relationship between outside indications of intelligence, such as school performance, and the measures used. His tests had more to do with physical coordination and strength than intelligence and as such had no construct validity. Later tests also had problems with validity but these were more subtle. For the most part, they were extremely culturally biased, serving the anti-immigrant bias of the first several decades of the twentieth century. Here the biggest problem was generalizeability, meaning the applicability of the test to a larger population. There was no consideration of English-speaking ability or of culturally relevant knowledge. Some items only measured knowledge available to wealthy, English-speaking, and native-born Americans. Other items measured moral values more than strict intellectual skills. Later IQ tests addressed these problems by including non-verbal tests, considering cultural relevance when including items, and basing test norms on samples carefully constructed to match the demographics of the United States.
