These claims have produced strong reactions from many people, including most psychologists and sociologists. They point out that the idea of associating race with intelligence levels is not only dangerous, because it encourages feeling of racial prejudice, but also based on misunderstandings about "race" and "intelligence." The word "race" as used by the great majority of people, has no exact, scientific meaning. When we talk of racial groups such as Negroes, Europeans, Jews or Chinese, we are really talking about social groups. The differences in personality between people from such groups are due mainly to the influence of social forces, not to the effects of biological factors. Intelligence is not something that can be measured exactly. Intelligence tests have been design to compare the intelligence levels of individuals in particular societies, but these are not always suitable for use among people whose social and cultural background maybe quiet different. Intelligence is also affected by health factors, especially in early childhood and at school interest, and encouragement are often just as important as a pupil's level of intelligence