Breaking Down the Wechsler Adult Intelligence Scale (WAIS)
What does it mean to be a genius? What's the deal with IQ averages and percentiles? How is IQ even determined, and why can it be a matter of debate?
There's a lot to unpack about how intelligence is measured, including how that process has changed over time. You might be surprised to learn about its many complexities! Let's take a look at IQs, IQ tests, and how the Wechsler Adult Intelligence Scale (WAIS) fits into it all.
The History of IQ Tests
If you're interested in IQ tests, the first thing to know is that there are many different kinds, including:
Stanford-Binet Intelligence Scale
Wechsler Adult Intelligence Scale
Peabody Individual Achievement Test
Differential Ability Scales
The concept of a test measuring one's intelligence quotient (IQ) was first invented by a French psychologist named Alfred Binet in the early 1900s. He had been tasked by the French government to find a way to identify schoolchildren who were falling behind academically or developmentally. In response, he created a test for various types of cognitive function, weighing the results on what he called the Binet Intelligence Scale.
In 1916, a psychologist at Stanford University created a modified version of the test called the Stanford-Binet Intelligence Scale. This new exam broadened its focus to rank those who excelled as well as those who under-performed. It was based on a set of timed tasks with scores that were aggregated into a single number representing a person's IQ.
The Stanford-Binet Intelligence Scale quickly took off across the country. It was even used by the U.S. military as a recruitment standard during World War I! People everywhere were excited to know how "smart" they were.
However, the test wasn't without controversy. In the 1930s, a psychologist named David Wechsler argued that it was designed for children, not adults, so it was missing key components in its assessment of cognitive function. He also disagreed with the idea of intelligence as a fixed concept that could be timed, measured, and scored with a single number.
This was the beginning of the Wechsler Adult Intelligence Scale.
What is the Wechsler Adult Intelligence Scale?
Created in response to the more rigid nature of the Stanford-Binet tests, the Wechsler Adult Intelligence Scale (WAIS) was designed to be more fluid and flexible. For example, rather than spitting out a single IQ score, it offers several scores that measure things like working memory, processing speed, and verbal comprehension.
The WAIS was also created for older adolescents and adults instead of schoolchildren, so it had broader applications for businesses and other areas of life outside of K-12 classrooms.
Another key difference between the WAIS and other IQ tests is how its numbers are determined. With the Stanford-Binet, scores are calculated by dividing the test taker's "mental age" with their "chronological age." With the WAIS, on the other hand, scores are calculated by comparing the test taker's results with other results from their age group.
What Gets Tested on IQ Tests?
Binet and Stanford-Binet
The earliest version of Binet's test, the one from 1905 that was meant to identify learning disabilities in children, measured more than two dozen cognitive skills. These included:
Verbal knowledge of objects
Execution and imitation of simple commands
Comparison of two weights
The drawing of a picture from memory
Objects to be placed in order
Replies to abstract questions
The naming of designated objects
The revised Stanford-Binet test included many of these tasks and objectives but added a timer to score them. However, there were aspects of both tests that were problematic. For example, one question asked "Which of these faces is prettier?" while showing sketches of a "normal" face paired with a "deformed" face. Other questions involved things like paper-cutting, which could be impaired by a child's motor skills but have no reflection on their actual intelligence.
The WAIS test incorporates similar tasks related to cognitive and executive function. Upon completion, however, the scores from the test aren't aggregated into a single number. Instead, they're divided into sections:
Verbal Comprehension Index (VCI)
Perceptual Reasoning Index (PRI)
Processing Speed Index (PSI)
Working Memory Index (WMI)
These measure each skill distinctly, which can be helpful for identifying the strengths and weaknesses of a person's mental acuity. The separate tests are also better at recognizing learning disabilities that only impact a particular kind of cognition. For example, an autistic individual might be non-verbal but in possession of an exceptional working memory.
The WAIS does provide an overall IQ score called the full scale IQ (FSIQ). This is based on the total combined performance of all four categories above. It also provides a score based on perception reasoning and verbal comprehension; this is called the general ability index (GAI).
The difference between WAIS and other tests is that it doesn't provide your FSIQ in a vacuum. Rather than saying "you're a genius because you have an IQ of 140," it'll provide a detailed analysis on the ways in which you rank higher and lower than your peers.
Generalized Vs. Fluid Intelligence
Another noteworthy thing about the WAIS test is that it provides a more accurate assessment of the two types of intelligence: fluid and crystallized.
These types of intelligence were identified by psychologist Raymond B. Cattell in the 1960s. You might be most familiar with his work on the 16 personality types that make up the modern-day Myers-Briggs Type Indicator (MBTI), but before his work was used for personality tests, it was breaking ground on classifying and categorizing intelligence.
As proposed by Cattell, there are two types of intelligence:
Fluid intelligence, or Gf, is based on your ability to reason, to think abstractly, and to solve problems. It's the kind of intelligence that you use when approaching new and novel situations and figuring things out.
Crystallized intelligence, or Gc, is based on your ability to retain and recall knowledge. It's the kind of intelligence that you can grow through education, experience, and everyday life.
A good IQ test will measure both fluid and crystallized intelligence to form a picture of one's generalized intelligence (G). In other words, Gf + Gc = G. However, not EQ.
Since the WAIS tests everything from inductive reasoning to spatial understanding and pattern recognition, it's generally seen as the superior test for measuring both types of intelligence. Its diversified results also allow for weaknesses to be identified in either category.
The WAIS Today
David Wechsler's intelligence scale was released in 1939. He used it to create his first intelligence test, the original WAIS, which was released in 1955.
There have been three other versions since then: the WAIS-R (1981), the WAIS-III (1997), and the WAIS-IV (2008).
The WAIS-IV is the version used today. It's become the most widely-administrated IQ test in the world, one that's seen in schools, universities, businesses, military institutions, and more. It's even spawned other versions for children and toddlers. In a way, the history of the IQ test is a circle!
If you're looking at IQ tests and wondering which is the best, the answer is generally understood to be the WAIS. While it isn't perfect, it's the result of years of research built off the foundation of other, more flawed tests, and it's flexible enough to allow for a broader understanding of how intelligence works and how it should be measured.