What is an IQ test?
An IQ test is a psychometric tool used to measure and quantify intelligence (someone’s reasoning ability) through a series of reasoning items.
IQ tests provide a score – that is, a quantification of intelligence-, that indicates someone’s level of intelligence. IQ tests are the type of psychological tests that are administered most frequently.
Additionally, IQ tests usually consist of several batteries or subtests, aiming to measure different cognitive sub-abilities, in order to generate a more comprehensive and detailed result of the test-taker’s mental abilities.
Knowing the score of the test-taker in each of these cognitive abilities can be of great help to fully understand his personality and his needs. It can give very useful insights and valuable information.
Currently, the most commonly administered tests are the Raven’s progressive matrices and the Wechsler scale of intelligence.
They can be taken both in person with a psychologist or online, though you will always have to take it through a licensed professional for any of the two.
Indeed, in some countries being a psychologist is not enough to be allowed to legally test IQ and perform official and diagnostic assessments, it is also necessary to receive a special training, qualification and license in IQ testing and in the particular test that the professional will use.
In order to really understand what these scores mean, we encourage you to have a look at our other articles on intelligence.
What do IQ tests measure?
IQ tests measure reasoning ability, also referred to as general intelligence or IQ. In turn, intelligence could be defined as the human ability to reason, think logically, find patterns in the information and learn. IQ also correlates with important life outcomes, such as academic performance or professional success, thus it is also fair to say that IQ tests can also measure and predict people’s success and performance in the said areas.
Although IQ and general intelligence (also called G) are not exactly the same, they are quite similar from a psychometric point of view, and one can more or less be used as an estimate of the other.
Along with intelligence, IQ tests can measure other sub-cognitive abilities, such as working memory or spatial intelligence, providing a full cognitive profile of the test-taker.
The final IQ or general intelligence score is usually a composite of all these subscores, and each of them has its own weight when performing the final calculation of IQ.
How does IQ testing work? How are IQ tests administered?
Usually, IQ tests are administered in person by a professional in a calm and quiet environment, free of any noise and distractions.
The professional – usually a psychologist with an official license to administer the IQ test he is using – will give all the necessary instructions about the test, and make sure everything is understood by the test-taker.
The process does not have any more secrets; after the instructions are given, the testing process can begin.
The professional will discreetly observe and study the test-taker while he is taking the test, and might take notes about his behavior.
He will ensure that there isn’t any bias on the part of the test-taker that could influence the final score (eg: stress, anxiety, the fact that some questions could have been misinterpreted or not understood properly, etc…).
In addition, some IQ tests can also be taken with a computer, either with the presence of a psychologist or completely online.
Choosing one type of administration method over the other (whether to take it in person or online) is usually up to both, the psychologist and the test-taker.
In some instances, doing it online could be the best administration method, since it would reduce all the stress and nervousness some test-takers have, and which might be exacerbated by the mere presence of the psychologist.
What different IQ tests are there?
Besides the Raven’s progressive matrices and the Weschler, these are the other iq tests that are still used nowadays:
- Cognitive Assessment System
- Kaufman Assessment Battery for Children
- Stanford-Binet Intelligence Scale
- Universal Nonverbal Intelligence Test
- Wechsler Adult Intelligence Scale
- Wechsler Intelligence Scale for Children
- Woodcock-Johnson Tests of Cognitive Abilities
Each IQ test has its own scoring rules, as well as its own framework and approach to measuring intelligence. However, all of them show very high correlations among them, which means all of them are almost equally valid for measuring intelligence, and it does not matter which one you take; your score will be very similar in each.
You can also click here to find more about the types of IQ tests that there are
What are IQ tests used for?
IQ tests are used for a variety of things.
- Educational assessment and placement
- For diagnostic purposes; in order to diagnose or to help to improve the resolution of the diagnosis of certain psychological problems.
- Psychological and sociological research
- In human resources, in order to evaluate candidates’ potential to perform well in the job
- Their scores can be used as admission criteria for certain schools, institutions, or groups, like Mensa.
How are IQ scores calculated?
IQ scores are calculated by comparing each test-taker’s performance in the test against the performance of his normative population, that is, by comparing his number of correct answers against the number of correct answers of the other test-takers of the same age and gender.
IQ scores are standarized, this means the mean is always set to 100. This number was set arbitrarily, and it is used just by convention. Their standard deviation is usually 15, which is also a number set by convention.
You can have a look at the entire IQ scale here, where we also explain its meaning in more detail.
IQ scores are also ordinal scores. In continuous variables, the quantitative differences between values are always equal to the same difference in the underlying thing being measured, that is, there is a direct and proportional relationship between the numerical amount and the magnitude of the thing being measured (Eg: height, weight, etc…). The difference between 100cm and 200cm is the same as the difference between 500cm and 600cm.
On the other hand, In ordinal variables, the difference between an IQ score of 150 and an IQ score of 140, is not the same as the difference between 100 and 110.
Same as with, for instance, satisfaction ratings. We certainly know that “Very satisfied” means “a higher degree of satisfaction” than “slightly satisfied”, but we do not know to what exact amount/quantity of satisfaction that equals.
Last, IQ scores follow a normal distribution. This means that most scores fall within a certain range around the mean. In the case of IQ scores, 68% of them lie between 85 and 115.
In order to better understand what an IQ test is and how its scores work, it is also important to understand what a standard deviation is.
A standard deviation represents the degree of spread/variability in a set of measurements/observations. If the standard deviation was 1, that would mean that all the scores are extremely concentrated around the mean, around 99 and 101.
It is calculated following a series of mathematical procedures, and it also indicates the percentile, that is, the percentage of observations (of people) who have a score equal to or lower than the actual score. Each standard deviation equals to a determined percentile (Eg: 115 equals the 84th percentile; it is above 84% of all the scores).
Indeed, the standard deviation is what gives the entire sense and meaning to the IQ scale and to the scores.
This is because almost any score can be expressed as a standard deviation (Eg: If your score is 115, you can just say that you score done standard deviation above the mean if it is 107, you could say you scored 0.5 standard deviations above the mean, and so on).
If the standard deviation is just a numerical way to represent a percentage, then that means that the entire IQ scale is just a numerical representation of a frequency distribution.
Which is essentially what it is.
That is why it is ordinal; you know that someone who scored better than 80% of the population is smarter than someone who scored better than 70% of the population, but you do not know what that difference means, you don’t know what the real quantity difference between the two scores is.
Having said all of this, you already know everything you need to interpret IQ scores!
You might still wonder how it is possible that the mean score can be magically transformed to 100, as well as the Standard deviation to 15.
In order to do that, psychometricians take the mean number of right answers of the test-takers, and then apply a series of mathematical transformations to make that amount equal to 100.
Getting into the exact mathematical procedures that are used is something that is outside the scope of this article.
Muhammad Ovais is Ph.D. from Chinese Academy of Sciences (CAS), National Center for Nanoscience and Technology of China. His research interests are in Neurodegenerative diseases, Nanomedicines and Biomaterials. He is the recipient of over 30 international awards including, 2019 Outstanding International Researcher by the Ministry of Education, China and 2019 Premium Award for Best Research Paper by IET-Institution of Engineering and Technology, UK. He owns to his credit over 60 scientific articles including research studies, reviews, editorials and book chapters in peer-reviewed journals/publishers such as, Advanced Materials-Wiley, NanoToday-Elsevier, Nanomedicine-Future Medicine, with h-index of 30. He is the co-founder of Synthon Nanotech, a Netherlands based Startup Company developing peptides and also working as a Tech Ethicist for a US based company GenoEmote; that is developing novel Brain-Computer Interface technologies.