The issue of intelligence remains one of the most controversial subjects in psychology. This controversy often centres on the contrast between the breadth of the construct and the specificity of the measurement tools. The Oxford Thesaurus for example includes the following synonyms for intelligence: “clever, bright, sharp-witted, smart, capable, knowledgeable, and brainy” – all of these are significant constructs in the study of differences between people. Few will argue that the speed with which people process information and solve various reasoning problems is significant. However, the issue of “what is intelligence” becomes controversial when we start saying that some people have more of it than others.
Alfred Binet (1857-1911) and the French school of intelligence first proposed that intelligence was an average of related cognitive abilities. Subsequent research by Charles Spearman (1863-1945) indicated a common function which he called general intelligence (g), and that there was overlap between each specific abilities and that an overall (g) measure which correlated highly with school performance. Later, the Harvard professor Raymond B Cattell (1905-1998) popularised the distinction between fluid (abstract performance IQ) and crystallised (academic or Verbal IQ) capability. Fluid assessments of intelligence such as performance IQ have been proposed as being more culturally fair than assessments of crystallised intelligence which it is argued merely reflect differences in educational opportunity existing between groups.
The illustration on the right shows how the Wechsler scales include measures of verbal (crystallised) and performance (fluid) IQ. This is one of the most comprehensive clinical assessments of intelligence. Although it is not suited to group testing and so is less popular in cost focused occupational environments.
In 1995 amidst controversy over reported racial differences in intelligence the Board of Scientific Affairs of the American Psychological Association (APA) issued a statement on the nature of intelligence. Intelligence is concerned with how… “Individuals differ from one another in their ability to understand complex ideas, to adapt effectively to the environment, to learn from experience, to engage in various forms of reasoning”. The Board of APA highlighted that while intelligence can never be measured entirely consistency, the most consistent research is based on standardised testing.
One of the most quoted answers to the question “what is intelligence” was provided by Edwin Boring in 1923 “Intelligence is what is what is measured by intelligence tests”. The measure of intelligence established by these assessments is commonly referred to as Intelligence Quotient (IQ). IQ is distinguished by it’s:
• Variance within a population
• Stability over time within an individual
• Prediction of Educational and Career Advancement
The diagram on the right shows the hypothetical distribution of IQ within a population. Binet also established the stable and fixed relationship between age and intellectual capability. Binet noticed that as children got older the relationship between their mental age and chronological age stayed the same. This means if I have a mental ability of a 6 year old at the age of 5 then I will have the mental ability of a 12 year old at 10 years. Binet created a formula to demonstrate this discovery (IQ= MA/CA X 100). Using this formula a 10 year old with the mental ability of an average 10 year old will have an IQ standardised at 100. Using the formula we can define the IQ of a 10 year old with a mental age equivalent to an average 12 year old. The formula suggests their IQ is 120. An IQ over 120 is assumed to be indicative of the requisite general ability for an honours academic degree. An IQ of over 140 is considered to be a genius. The formula also highlights the important idea that the distributions of performance does not change significantly as we age. If an individual is better than 95% of his peers at numerical reasoning Binet predicted he would be ahead of 95% of his peers at 18 years of age. Beyond the age of 18 he assumed our abilities are fully developed. The concept of how performance is distributed and using this concept to interpret individual differences is fundamental to standardised scoring and interpretation.
The Flynn Effect
Although intelligence tests have proven to have the ability to predict an individual’s performance over time there are some outstanding questions raised by research in this area. Differences in performance of blacks and whites in the US on intelligence tests are highly controversial. However, perhaps the most intriguing research conundrum is that identified by James Flynn. Flynn (2007) has documented a substantial increase in average scores on intelligence tests all over the world. The average rate of increase seems to be about three IQ points per decade in the US on tests such as the Wechsler Intelligence Scale for Children (WISC). The increasing raw scores appear on every major test, in every age range and in every modern industrialized country although not necessarily at the same rate as in the US using the WISC. The increase has been continuous and roughly linear from the earliest days of testing to the end of the twentieth century. Interestingly, there is evidence that the increase has abated in the twenty first century. Ulric Neisser estimates that using the IQ values of today the average IQ of the US in 1932, was 80. Neisser states that “nearly one-quarter of the population would have appeared to be ‘deficient.'” He also writes that “Test scores are certainly going up all over the world, but whether intelligence itself has risen remains controversial”. Attempted explanations have included improved nutrition, a trend toward smaller families, better education and greater environmental complexity. Another proposition is the gradual spread of test-taking skills. What do you think?