Standardized Testing

Standardization and the Intelligence Quotient

These days, intelligence quotient (IQ) is used to denote general intelligence or a score on any intelligence test. However, it was originally the name given to the score of the Binet-Simon test. That score was calculated by dividing a child’s mental age (the average age of someone who scored the same as the child on the test) by their chronological age and multiplying by 100 to create an overall quotient. However, the ratio IQ of mental age is no longer used for scoring intelligence tests.

Instead, intelligence tests are now standardized and can give a deviation IQ score that compares a person’s test score to the average score of others on the test; in other words, how much does an individual’s score deviate from the average. After a large sample of people take an intelligence test, scores are plotted and a normal distribution shaped like a “bell curve” emerges (see Figure 8.2). To understand a normal distribution think about the height of people. Most people are average in height with relatively fewer being tall or short, and fewer still being extremely tall or extremely short. There is a similar pattern for intelligence; most people have about average intelligence (IQ = 100), while very few have extremely high or extremely low intelligence.

Because the standard deviation of an IQ test is about 15, this means that roughly 2% of people score above an IQ of 130, the usual threshold for giftedness, and about 2% score below an IQ of 70, the typical threshold for intellectual disability.

Using a deviation IQ is particularly helpful in comparing a child’s performance to the average of other children of the same age.

It is important that intelligence tests be re-standardized on a regular basis, because the overall level of intelligence in a population may change over time. The Flynn Effect refers to the observation that intelligence test scores worldwide have increased substantially over the past decades (Flynn, 1999). Although the increase varies somewhat from country to country, the average increase is about 3 IQ points every 10 years, meaning that people are more intelligent with each generation (Flynn, 1999). There are many explanations for the Flynn effect, including better nutrition, increased access to information, and increasing familiarity with multiple-choice tests (Neisser, 1998).