The Wechsler Intelligence Scale is the most precise intelligence test that exists today, both for adults (WAIS-IV) and also in its children’s version (WISC-V). We will explore its main characteristics, history, versions, types of questions, and much more. In less than 10 minutes of reading, you will be familiar with its most important traits and how its strengths and weaknesses differentiate it from other tests.
The Wechsler Scales have a long history, and have been subject to several renewed editions by the best psychologists in the field. Currently in its fourth edition from 2008 (fifth for the children), it is used by 90% of psychologists that evaluate intelligence. The scales check different cognitive abilities through 10 core subtests and five optional subtests depending on the psychologist’s choice.
The different subtests are summed up into four indexes which together comprise the Full Scale IQ (also known as the global IQ). These indexes are (i) verbal comprehension, (ii) perceptual reasoning, (iii) working memory and (iv) processing speed.
To achieve its robustness, it can't help it but be a quite lengthy test. Taking at least 90 minutes, it requires good effort by the psychologist. No surprise it is much more expensive. But its reliability makes it worth it, especially when it is important to discover the different strengths of the person.
The test can be done by persons age 16 to 90 year old, but up from 70 some modifications are necessary, like the increased weight that ought to be given to arithmetics.
How it all began
Everything began in 1939, when David Weschler, a psychologist working at the NY Bellevue Psychiatric Hospital, created a new intelligence test out of his dissatisfaction with the Stanford-Binet option. Contrary to common belief, he did not innovate that much, as his test was more than anything a very careful selection of the different tasks of other tests available at that time (Army’s tests, Stanford-Binet, etc.).
Wechsler thought that using only verbal tasks as Binet did, discriminated against people with strong reasoning but weak language. His multiple-task battery solved the problem by evaluating several additional abilities. Keep in mind however that Wechsler never talked about the existence of different intelligences in the way Gardner today defends his multiple intelligence theory, but he saw them as manifestations of our unique intelligence.
Maybe because of his lack of data for supporting the addition of non-verbal questions, he was rejected several times by publishers. And even after getting to the public, it was not until the late 60’s that the scale started receiving its merited attention.
As the test became increasingly famous, several versions with improvements were made, both to the adult and the children scales, until reaching our current fourth and fifth version respectively. Even a scale for very small children (WPPSI) was pretty soon developed and has been improved through the years.
The impact of the test on clinical and educational contexts has grown slowly but has reached in the present such a dramatic level, that Wechsler is considered to be the psychologist with the most real-life impact on people to have ever lived.
Types of Questions
Now that you know the basics, you might be wondering what the questions look like. Let us look at the subtests that make it up, grouped by their respective index.
1. The Verbal Comprehension Index is designed to measure concept formation and verbal reasoning. It is made up of four subtests:
- Similarities: where you need to find the common aspects of two words. Eg. What makes oranges and bananas similar?
- Vocabulary: you need to come up with the most appropriate words.
- Information: you are tested on general knowledge. Eg. Which is the capital of Japan?
- Comprehension: optional subtest, with a multiple-choice format to check if things are well understood. It helps a lot in finding personality problems.
2. The Perceptual Reasoning Index is intended to measure how well you operate figures and forms, detect patterns, and reason about them. It is made up of five subtests:
- Block design: you have to find the pieces that make up a figure.
- Matrix reasoning: you see a matrix with several figures but one missing. You will have to choose which figure completes the matrix while fitting possible patterns best.
- Visual Puzzles: self-explanatory right?
- Figure weights: you see an imbalanced balance, and you need to find which figure restores it. Optional.
- Picture completion: optional subtests, where you have to find the missing piece for the picture.
3. The Working Memory Index measures the ability to store and operate numbers and letters. It is made up of three subtests:
- Arithmetic: you have to solve as many basic problems as possible within the time limit. There are no complex math problems.
- Digit span: you are read sequences of numbers (eg. 1,3,5,2,7) and you have to remember them forward or even backward. This task is very helpful in finding low IQ and clinical problems.
- Letter-number sequences: the same, but also with letters. Optional.
4. The Processing Speed Index as its name reveals, measures the speed in processing information. It is made up of three subtests:
- Symbol-search: you must scan and find Wally :). Of course not. You are given a symbol and you must check if it is in the group.
- Coding: checks the ability to copy symbols.
- Cancellation: same as symbol-search but with shapes. Optional.
Summing up the four indexes you get the Full Scale IQ (FSIQ). And if you do not want to take into account working memory and processing speed, you can compute the General Availability Index (GAI) summing up the first two indexes. Short-term and long-term memory indexes can also be computed.
When should the Wechsler test be used?
The Scale, due to its broadness and quality, can be used for nearly any conceivable purpose. Firstly, it is the best option for clinical and neuropsychological evaluations. Second, it helps schools to detect children that need special education, be it in terms of additional assistance when relevant weaknesses are found, be it in the form of harder and faster training for genius kids. And third, even in the talent acquisition arena, it is used to ascertain the intelligence of potential candidates.
The test is ideal for clinical use because its evaluation of different abilities gives a really comprehensive picture of the person. The different strengths and weaknesses often confirm or hint at a specific clinical diagnosis, while at the same time paving the way to find out the most beneficial treatment depending on the skillset. Significant discrepancies between verbal and non-verbal tasks is a common example that usually leads to the discovery of some type of pathology.
Validity and reliability
So, why is the test robust? More than 2.200 people helped in the test creation by taking the test themselves. By definition, the test has an average of 100 (10 for each subtest) and a deviation of 15 (3 for each subtest). As said earlier, usually only 10 subtests are employed for scoring.
If a test offers the same results to the same person under similar circumstances, in other words it is free of measurement error, we say it is reliable. It is a very important trait of a test. Or would you have confidence in a test that gives you a different result if you try again in 20 days without discovering the answers in the meanwhile? Well, in this aspect, the Wechsler is highly reliable. Both looking into any specific subtest, as well as checking the global index scores, they all have excellent reliability (around 90%), making it the best intelligence test available.
The validity, whether the score means something in real life, is also pretty good. It has been found that the Full IQ that you obtain, is related up to 90% to the level of academic achievement. So a good score on this test will never guarantee success, but it predicts a good probability of doing well in school or work.
And there is more to this. A handful of subtests (Arithmetic, Figure Weights, Matrix Reasoning, Vocabulary) are better indicators than other subtests of the Full IQ that the person has. Be careful, however, since most psychologists do not think the Full IQ is the really important metric. They put more focus on the level achieved for each ability and how each differs from the rest, which will give a picture of the person's strengths and weaknesses.
Remember we said that the test can be quite expensive and time-consuming? For such a reason, several experts have proposed shorter versions that take up to 50% less time, where either only some subtests are done, or all of them have fewer items (or both strategies combined).
Studies have shown that when comparing the short and long versions, the results are nearly 90% similar. The strategy has been so successful that now approximately 30% of all Wechsler tests carried out, use some shortened adaptation.
One short version pretty extended is made up of the subtests: similarities, arithmetic, vocabulary, block design, and visual puzzles, while skipping the rest. As you guess, the test is way faster to administer.
Strengths and weaknesses
Regarding its weaknesses, we can highlight that: it is time-consuming, although the shorter versions mitigate this problem. The price is usually pretty high in most countries. And some subtests are ambiguous and difficult to score objectively. Finally, the test is quite complex to deliver and only a specialized psychologist can do it in person.
As its strengths, we can count: excellent reliability and validity, evaluating the full spectrum of cognitive abilities; the fact that the adult and children versions have similar tasks what makes them easier to compare, and last but not least, it fits pretty well with the most accepted theory of intelligence, the Cattell-Horn-Carroll (CHC) model.
All in all, the Wechsler scale is a fantastic intelligence scale that you should probably have as the first option for any important purpose like clinical evaluation. If you only want a simple IQ exploration, then using an abbreviated form of this test is a great option too. It clearly outperforms its competitors in mostly everything. But if what you need is a fast, easy-to-deliver, and low-cost test, then we would recommend other possibilities, like the Cattell Culture-Free Test, which you can take with us online.