Average IQ scores from different ethnic groups vary, and these statistics have led to much controversy. According a report by the Board of Scientific Affairs of the American Psychological Association, African-Americans had low mean IQ scores, approximately 15 points below those of whites. Native American and Hispanic children were also found to have a lower average IQ to Whites. Asians, namely Japanese and Chinese-Americans, were about average to whites. These groups differences may be due to socioeconomic reasons or general test bias.
Socioeconomic status involves a person's general income level, educational attainment and social class. This environmental difference affects IQ scores. Persons with higher education and income have a higher average IQ. Persons with more complex jobs, such as professionals, had higher scores than low skilled workers. Neglected children have lower IQs, and rural inhabitants had lower scores than those residing in urban areas. According to the Board of Scientific Affairs of the American Psychological Association, children who were sent to preschool intervention programs for low income families, such as "Head Start" had little difference in IQ than poor children who did not attend an intervention program.
The health of a person affects his IQ score. Illnesses such as Alzheimer's lower IQ scores. Poor nutrition, especially prenatal nutrition, has a major effect on cognitive development. Low birth weight correlates with lower IQ scores, and toxins, such as lead, has negative effects on IQ scores. Genetic disorders such as Down Syndrome also plays a role in lowering IQ. Research has also shown that mothers who drank heavily during their pregnancy had children who scored about 5 points below average. Prenatal aspirin and antibiotic exposure had the same effects.
Standardized IQ tests are constructed so that there is no gender difference in scoring. Men tend to score higher in mental rotation tasks, such as tracking a moving object in space. Female children show higher quantitative abilities than boys on IQ tests, but after puberty this ability shifts. Men consistently score higher on quantitative abilities and on tests of proportional and mechanical reasoning, which is used in mathematics. Women have higher verbal abilities and score higher in spelling and reading. Women who were given higher amounts of the female hormone estrogen performed better a some skills, while men who were given the male hormone testosterone improved in visual-spatial tests.