IQ Scale (A comprehensive Guide)

This guide brief about IQ scale, how they are developed and how they can be scored.

Human intelligence refers to the cognitive ability to learn from experience, adapting to new circumstances, knowing and interacting with abstract concepts, and using information to influence one’s surroundings.

Most of the enthusiasm in the field of intelligence among investigators stems from their efforts to identify exactly what intelligence is.

In their definitions, different investigators have highlighted various elements of intelligence.

For example, the American psychologists Lewis M. Terman and Edward L. Thorndike disagreed in a 1921 symposium on the definition of intelligence, Terman emphasized the capacity to think analytically, while Thorndike stressed learning and the ability to answer questions in a good way.

Nevertheless, more recently, psychologists have widely accepted that the key to understanding what intelligence is and what it does is to adapt to the environment.

Successful adaptation is based on a variety of cognitive processes, including perception, reading, memory, reasoning, and problem-solving.

Therefore, the main emphasis in a definition of intelligence is that it is not a cognitive or mental process, but rather is a specific blend of these processes intended for effective adaptation.

Intelligence Quotient

To relate the mental development of a child to the child’s chronological age, the IQ scale was invented.

An IQ scale is a total score obtained from many standardized tests intended to evaluate human intelligence.

The abbreviation “IQ scale” was created from the German word “Intelligenzquotient” by psychologist William Stern, a concept he proposed in 1912 in a book for a ranking system for intelligence testing at the University of Breslau.

Traditionally, IQ scale is a score acquired by dividing the mental age score of a person, collected through the administration of an intelligence test, by the chronological age of the person, both expressed in terms of years and months.

To obtain the IQ scale score, the resulting fraction is multiplied by 100.

“IQ scale” assessments were initially created in order to recognize children who may need special education.

The test by Binet included a variety of questions and activities. Even the unwrapping of a piece of candy and measuring the weights of various items were included in the tasks.

IQ scale scores are used for academic selection, intellectual disability assessment, and work applicant’s evaluation.

Even if students improve their scores on standardized tests, their cognitive abilities, such as memory, attention, and speed, are not always improved.

Because people wanted to use IQ scales for adults as well, this equation was not very successful because raw scores start to drop off around the age of 16.

Thus the deviation IQ scale replaced the ratio IQ scale.

This measures people of the same age or age group and assumes that IQ scale is normally distributed, the average or mean is 100, and the standard deviation is about 15.

IQ scale tests sometimes differ in their standard deviations.

What is the standard deviation (SD)? Simply put, the standard deviation is a measure of the spread of the sample from the mean.

As a rule of thumb, about 2/3 of a sample is within 1 standard deviation from the mean.

About 95% of the sample will be within 2 standard deviations from the mean.

You can calculate percentiles using the standard deviation and a mean.

Percentiles shows you the percentage of people with a score that is equal to or below a certain number.

High IQ scale societies ask you to be eligible to join them for certain percentile scores on IQ scale testing.

What it Measures

IQ scale testing is designed to measure the overall problem solving and comprehension of concepts.

It includes the ability to think, the ability to solve problems, the ability to perceive connections between objects, and the ability to store and collect information.

In a number of ways, IQ scale tests assess the basic intellectual ability.

These include the following:

  • Spatial skill: the abstract ability to visualize manipulation shapes
  • Mathematical skill: the ability to use logic and solve problems
  • Language skill: this could include the ability to complete sentences or remember words while rearranging or deleting letters.
  • Recall capacity: the ability to remember items mentally or aurally

Questions are designed in a way that checks for a particular cognitive ability in each of these groups, but many researchers claim that they also reflect general intellectual ability.

Some people perform well in one type of category than on others, but researchers have concluded that, for the most part, people who succeed in one category do equally well in other categories, and if someone does poorly in one category, they do poorly in the other categories.

Some researchers theorize on this basis that there is a common element of intellectual ability that defines certain unique cognitive abilities.

Ideally, an IQ scale test tests this general intelligence element, which is abbreviated as g.

Classification Systems

There are a variety of classification systems for IQ.

Terman’s classification was:

IQ RangeClassification
140 and overGenius or near genius
120-140Very superior intelligence
110-120Superior intelligence
90-110Normal or average intelligence
70-80Borderline deficiency
Below 70Definite feeble-mindedness

(Terman wrote the Stanford-Binet test, which has an SD of 16.)

However, Wechsler assumed that basing his classifications on the Probable Error (PE) would be much more appropriate, so his classification was:

ClassificationIQ LimitsPercent Included
Very Superior128 and over2.2
Bright Normal111-11916.1
Dull Normal80-9016.1
Defective65 and below2.2

Mental deficiency used to be categorized more precisely using the below technical terms that the rest of society later started to misuse

IQ RangeClassification
70-80Borderline deficiency
below 20Idiot

These are outdated now. In 2010, the words ‘ mentally retarded’ and’ mental retardation’ were substituted by Rosa’s Law legally by’ intellectually disabled’ and’ intellectual disability.’

The following was the classification of retardation prior to the fifth edition of the Diagnostic and Statistical Manual (DSM 5), which now uses the terms ‘ intellectual disability (intellectual developmental disorder).’

the following was the classification of retardation in the USA:

IQ RangeClassification
below 20Profound

Although IQ scale is still part of the evaluation (the threshold is 70 ± the measurement error of the particular test), the DSM 5 has replaced certain IQ levels with functional tests, theoretical, social and realistic criteria.

IQ scale is not adequate. Perhaps the same kind of thing should be done to mark a genius for someone.

IQ Scoring

Approximately 2% of the population has an IQ score below 69. Using a standard intelligence test is often difficult to measure such a low IQ score.

Also, very high IQ scores are difficult to accurately assess. This is because you need a lot of measurements of reference to reliably determine a particular score.

Just because very high and very low IQ scores do not occur often, such a reference group is difficult to form.

IQ Score by Age

While scores should always be taken with a pinch of salt by age or ethnicity, under certain conditions it may be useful to look at them.

There are no actual age-organized data, but some information on age groups is available.

The following information should be used for entertainment purposes only, as it may not be completely accurate and obsolete.

Also, data is available for people aged 16 to 74.

That might be because IQ tests for younger children are not advised unless a psychologist advises and directs them individually.

This being said, here are the average scores per age group on the IQ scale.

  • The average score for 16 to 17-year-olds is estimated to be 108, which refers to “normal or average intelligence.”
  • For adults between the ages of 18 and 19, the average IQ score is 105, which also refers to ‘ normal or average intelligence’.
  • The average score for people between the ages of 20 and 24 is 99, which also refers to ‘ normal or average intelligence’.
  • For people between the ages of 24 and 34, the average score is slightly lower at 97, which still refers to ‘ normal or average intelligence’.
  • After that age, the scores start to rise again among older adults. For example, the average score is measured at 101 for people between the ages of 35 and 44, still within the range of “normal or average intelligence.”
  • And for people between 45 and 54, in the “normal or average intelligence” scale, the average IQ score goes up to 106.
  • However the highest average score among people under the age of 64 is reached by those between 55 and 64 of age, who hit 109 in the IQ scale, only coming up short of being graded as possessing “superior intelligence” or “above average” intelligence and staying squarely inside the limits of “normal or average intelligence” like all other age groups.
  • A higher score is achieved for both age groups over 65. Adults between 65 and 69 have an average IQ score of 114, placing them at the “superior intelligence” or “above average” end of the scale.
  • Yet adults around 70 and 74 who are screened for IQ get a much higher average score of 119, that places them a mere 1 shy of joining the “gifted” class, meaning they are still solidly within the “above average” or “superior intelligence” group along with their younger counterparts aged 65-69.

This will come as no surprise to anyone that all age groups assessed often receive an average score because, as we have previously noticed, generally, many people who have their IQ tested get scores within that range.

What Is the Normal Distribution of IQ Scores?

If you don’t consider age, you may look at IQ scores more globally.

Did you know, for example, that about 50% of IQ is between 90 and 110?

Or that 70% get a score from 85 to 115? Surely these figures are enlightening.

 But wait, it gets more exciting. Roughly 95% of all IQ ratings are between 70 and 130. And, the overwhelming bulk of them (99.5 per cent) do fall someplace between 60 and 140.

Only people at the highest 2% of the IQ scale can be admitted to Mensa, the world’s biggest and most reputable high-IQ society, with participants in most countries worldwide.

We must treat IQ charts that categorized by age or any other criterion with extreme caution.

A factor for this is that we need to make sure that we keep it empirical and that there are no biases at all.

There are also a lot of different tests available, yet only a small minority of people will in actual take such tests.

And there is also the concern of mortality, which in different countries around the world still varies considerably.


Intelligence Quotient tells people about their mental level corresponding to their chronological age.

The test consists of four categories; spatial, mathematical, recall and language.

There are different levels of IQ based on different theories and chronological age.

Frequently Asked Questions for IQ scale Scale

What is considered a high IQ?

According to Terman’s Classification, scores of 140 or over are considered as highly gifted individuals.

What are the signs of low IQ during childhood?

The signs of low IQ in infants and children are that they will learn and develop slower compared with other kids.

Infants will roll over, sit up, crawl or walk developmentally delayed.

What was the IQ of Albert Einstein?

The IQ of Albert Einstein was over 160.

Can your IQ drop?

Yes, it is possible that your IQ drops with age but the IQ test scores will give you the same results.

Please use the comment section below to ask any questions you might have.


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