What does it mean to be “smart”? Determining what intelligence is and the methods used to quantify it have been researched for centuries. In the late 1800s, England’s Sir Frances Galton theorized that intelligence is hereditary and attempted to measure it by assessing subjects’ competencies on sensorimotor tasks. He was a pioneer in this field, one of the first to organize data collected by statistics, and even investigated whether head shape and size determined a person’s intellectual abilities (they didn’t!).

In the early 1900s, French psychologist Alfred Binet and physician Theodore Simon created a working definition of overall cognitive ability or “Intelligence Quotient” (IQ). They partnered to craft the first scale measuring overall intelligence: the Binet-Simon Scale. Policymakers in France had asked him to devise a way to determine which children would likely need more help in school. Binet and his team attempted to use their scale to measure attention, memory, and problem-solving skills. They obtained an overall cognitive score (IQ) by finding a subject’s mental age, dividing that by the chronological age, and then multiplying by 100. Other contributors toward the IQ concept included German psychologist William Stern and American psychologists Henry Herbart Goddard and Lewis Terman. Their input refined the definition of and measurement of IQ. However, Binet was not fully sold on the IQ method of measuring cognitive ability. As more people were assessed, he began to believe that one number to describe intelligence couldn’t fully be accurate, as the concept was too complex. He is quoted as saying, “Intellectual qualities … cannot be measured as linear surfaces are measured… [giving IQ too much significance] may give place to illusions. ”

In the mid-1900s, American psychologist David Wechsler led a team to create a series of cognitive assessments, currently known as the Wechsler Intelligence Scale for Children (WISC), Wechsler Adult Intelligence Scale (WAIS), and Wechsler Preschool and Primary Scale of Intelligence (WPPSI), all currently under varied editions. His IQ- termed Full Scale Intelligence Quotient or FSIQ- was obtained by comparing one subject’s score to a survey of others in the same age range, using a standard scale. This structure caught on. Several other psychologists have created other cognitive batteries in the years since: Differential Ability Scales (DAS), Kaufman Assessment Battery for Children (KABC), and Woodcock Johnson Tests of Cognitive Ability (WJ), for example, and they are periodically updated with norms and content. Some measures quantify IQ with slightly different terminology, such as General Intellectual Ability or Fluid Crystallized Index. These batteries assess some or all of the following abilities that constitute the overall IQ: Crystallized Knowledge Gc, Fluid Reasoning Gf, Short-Term/Working Memory Gsm, Long-Term Retrieval Glr, Auditory Processing Ga, Visual Processing Gv and Processing Speed Gs. (Different cognitive tests can be used with aging populations, as well, to assess for dementia or memory loss. Those assessments are not the focus of this article.)

Intelligence results have been used for a variety of applications. For example, the US Government uses assessments to distinguish roles within military personnel. Tests have also been used to screen immigrants entering the country and make judgments about the abilities of various people-groups. Cognitive testing results have also been used to argue that different races have varying intellectual capabilities. Some early researchers even proposed eugenics in an attempt to improve a population’s cognitive outcomes. Ultimately, ensuring the absence of cultural bias in the content and language of tests cannot be guaranteed. Because of the disadvantages for minorities in IQ assessment, attempts have been made to curb their use. In 1971, the state of California forbade the use of IQ results to place students of African descent into highly-restrictive classrooms through the ruling in Larry P v. Riles. This ruling persisted despite appeals and has since been broadened to ban IQ assessment of all Black students being referred for special education services. Whether or not this is the best plan for disabled students of color in California is debatable. However, it is critical to be mindful of racial disparities in cognitive assessment. Research-rich articles arguing against the role of racial genetics in cognitive ability can be found here: 1, 2, and 3.

Results from cognitive assessments have also been used to deny special education eligibility to students in the state of Texas. Previous models of learning disabilities have required a connection between cognitive weaknesses and low academic achievement. The Texas Education Agency has increasingly made it clear that cognitive ability or lack of ability cannot deny students access to a free and appropriate public education.

IQs can be interpreted through two approaches: top-down or bottom-up. The top-down theory espouses the idea that all areas of intelligence are correlated and that the ‘general factor’ g – or IQ- is a good measure of overall intellectual ability. In the bottom-up approach, all areas of intelligence are analyzed to present a wider picture of a person’s abilities, including their personal strengths and weaknesses. Two people with the same IQ can have very different profiles, after all. There is also emerging comparison between normative and ipsative approaches to cognitive scoring. The normative method, previously mentioned, compares one person’s score to a norm of many other scores from testers of similar age. This results in a ranking of performances. The ipsative approach compares one person’s scores to their own varied performance and includes any past results, determining personal progress over time. This helps create intervention to strengthen areas that may be weak within an individual’s profile. Over time, norm-referenced assessment has faced increasing criticism. Stern, one of the pioneers of the IQ concept, became critical of normative approaches to intelligence measurement in his later career. American psychologist Alan Kaufman is a modern researcher and test creator who has embraced including the ipsative approach when understanding a person’s overall intelligence. 

In addition to complexities mentioned so far in this article, opinions differ on validity and reliability of cognitive testing in general. Many factors can affect an individual’s results: cultural and language differences, evaluator practices and competence, differences in socioeconomic status, and even a tester’s mood or health on the day of assessment. These factors, among others, can affect the testing outcome. Researchers and experts generally agree that cognitive tests currently in use are valid and reliable; however, it is important to be aware that controversy exists in this area.

Because intelligence is complex and variations occur across a person’s cognitive profile, it’s important to refrain from forming a judgment about someone’s prospects for success based solely on the results from an IQ assessment. Our understanding about intelligence has changed considerably over the last century- imagine what may develop over the next 100 years!