10.1 Intelligence

The controversy regarding racial differences in intelligence stems from the historical observations of average disparities in standardized IQ test scores. For example, IQ test results often showed that Asian individuals tended to score slightly higher than White individuals, and White individuals tended to score higher than Black individuals. Since 2006, studies using cognitive tests have shown a difference ranging from .8 to 1 standard deviation units between the means of the White and Black populations. Historically, the difference in scores between Whites and African Americans has been .35 standard deviation units; with earlier studies, the differences were larger (Hunt & Carlson, 2007).

One argument for racial differences in intelligence is based on Spearman’s hypothesis (Jensen, 1998). It was suggested that general intelligence (g)—a factor believed to represent a common underlying mental ability—is largely genetic and correlates with test scores. A statistical technique called the method of correlated vectors was used to determine the correlation between (g) factor and other variables of interest, such as the heritability estimate of the subtest of intelligence tests. However, critics argue that this correlation does not imply causation and that alternative explanations should be considered for the racial differences in intelligence scores.

Alternative explanations for variances in intelligence test scores include socioeconomic disparities, construct validity, the cultural context of IQ tests, and stereotype threats. Researchers suggest that examining the relationships between intelligence and both genetic factors and environmental factors is important (Hunt & Carlson, 2007). They argue that researchers should be cautious when making causal inferences about the relationships. Studying the racial differences in intelligence is reasonable, but researchers also propose that the principles of design, analysis, and reporting need to be carefully considered when conducting or evaluating research in this area.

Socioeconomic Disparities

Research found that, in young children, the heritability of IQ score varies inversely with socioeconomic status (SES). This means that environmental factors play a larger role in IQ scores in lower-SES families than in higher-SES families. In addition, factors such as parenting style and orderliness of the home, which are related to SES, can contribute to the development of children’s intelligence (​​Turkheimer et al., 2003). Thus, socioeconomic disparities may be able to explain the racial differences in IQ scores.

Construct Validity

Conclusions about intelligence scores rely heavily on the validity of measurements. The use of poor-quality data and questionable measures can lead to inaccurate conclusions. For example, Lynn and Vanhanen (2002) used IQ test scores to predict indices of economic productivity across nations. The study was criticized for utilizing IQ data collected from highly specific, nonrepresentative subgroups, such as children with developmental disabilities and immigrants, and generalizing this data to represent the average IQ of an entire nation, which made the construct validity questionable. Thus, measurement errors or biases in data collection can offer alternative explanations.

Cultural Context of IQ Tests

In different cultures, what is considered “intelligent” can vary. Research suggests that some culture-specific activities, such as traditional medicines and hunting practices, were not correlated with measures of general intelligence (Fagan & Holland, 2002). This indicates that test scores might reflect specific cultural knowledge rather than a universal cognitive ability, offering an alternative explanation for score differences between culturally diverse groups.

Stereotype Threat

Stereotype threat means that the examinee may perform worse if they believe that the social group that they belong to is stereotyped to “do poorly” on a task. Steele and Aronson (1995) found that when Black students were told that other Black students either did well or poorly on a test, the students performed similarly, and this manipulation was effective even after controlling for SAT scores. Although stereotype threat does not fully account for the racial differences in IQ tests, it offers a motivational alternative to cognitive deficit explanations for performance differences.

As discussed in the NOBA textbook, Francis Galton was one of the pioneers of psychological measurement. Galton, a cousin of Charles Darwin, was an English polymath and the originator of eugenics . He applied Darwin’s theory of natural selection to human society. He believed that intelligence is inherent and that society could use that information to encourage those who seem to be “fit” to reproduce more. Galton wondered whether measuring intelligence could be similar to measuring height and eye colors (Hunt, 2009). He eventually established that intelligence is a variable that can be measured.

However, Galton was not the first to seek to measure human intelligence. In fact, the earliest intelligence test was developed in China over 3,000 years ago and required people to write essays to determine if they were eligible to be hired as civil servants. The test was later expanded to include problem-solving tasks, making it similar to the modern intelligence test (Saklofske et al., 2015).

In 1905, decades after Galton published his theory of intelligence, the French government sought a way to identify children who might be struggling and need additional educational support at school. This prompted Alfred Binet, a pioneer of intelligence measurement, to develop the Binet-Simon test to measure children’s intellectual abilities, which he referred to as their “intelligence quotient” or “IQ.” Later, a modern intelligence test called the Wechsler Adult Intelligence Scale (WAIS) was developed. It addressed some of the issues present in the Binet-Simon test and measured a wider range of intelligence (Wechsler, 1955).

One caveat of the Binet-Simon test was that it should only be used to compare children with similar socioeconomic (SES) backgrounds because SES disparities could affect the results (Guthrie, 1998). However, a key idea of eugenics is that intelligence is primarily determined by genetics rather than environmental factors. In the early 20th century, belief in eugenics was widespread in Western countries, and many psychologists involved in developing intelligence tests were eugenicists. Some, like Henry Goddard, even argued that society should keep “feebleminded” people from having children (Goddard, 1912). As a result, intelligence tests were used to marginalize people with lower formal educational levels, including women, people of color, and people living in poverty (Guthrie, 1998).