What Is Intelligence & IQ?
Intelligence can be defined as “the global ability of an individual to think clearly and to function effectively in the environment“. By breaking down this definition, we can get a clearer understanding of exactly what intelligence is.
Global means that a person’s intelligence affects many areas of their life. For example, we think of smart people as people who are good at many things.
Think Clearly
Thinking clearly means the ability to use both inductive reasoning/inductive logic (i.e. determining what theories may explain your data) and deductive reasoning/deductive logic (i.e determining what else could be true based on what you already know) when forming conclusions, rather than doing so based on emotional responses.
The main feature of intelligence is the ability to use convergent thinking (i.e. putting different ideas or information together based on what they each have in common when trying to solve a problem), and this is something which can be tested for by using intelligence tests.
Function Effectively In The Environment
A person with intelligence is able to successfully interact with other people and things in their surrounding environment.
Types Of Intelligence
In the 1930s, a researcher by the name of Louis Thurstone created a factor analysis of intelligence which allowed for sets of data to be analyzed for trends.
As a result of his research, Thurstone concluded that there are nine primary mental abilities as is shown below.
• Inductive reasoning
• Deductive reasoning
• Word fluency
• Speed of perception
• Verbal comprehension
• Verbal fluency
• Memory
• Spatial visualization
• Mathematics
Expanding upon this view of intelligence was the psychologist Howard Gardner, who suggested that we have multiple types of intelligences.
The eight intelligences proposed by Gardner are:
• Verbal
• Logical
• Kinaesthetic
• Naturalistic
• Musical
• Visual
• Interpersonal
• Intrapersonal
As you can see from the descriptions of intelligence so far, intelligence can be viewed in both a broad perspective (a general/global ability), or as a set of specific abilities such as those proposed by Thurstone and Gardner.
What Is Intelligence?
Despite the theories that we currently have, intelligence is still something which is hard to accurately define. For example, a person may do poorly on their exams at school but then later in life goes on to create a successful business.
According to their exam results, this person displayed a low level of intelligence, but later on, demonstrated a high degree of intelligence by creating their own business.
So whilst an intelligence test may give us an idea of what a person is likely to be good at, we cannot say for certain how intelligent a person is because different circumstances may have different effects on the type of intelligence that they display.
Another reason why we cannot completely define a person’s level of intelligence, is because intelligence has the status of a hypothetical construct.
This basically means that there are theories which help to explain intelligence, but we don’t know for sure exactly what intelligence is as it can vary depending on how you define it. Therefore, we can only make an educated guess based on the tests which we use to measure it.
These tests of course, may or may not reveal a person’s true level of intelligence and so run the risk of falsely labelling someone as being very intelligent or lacking intelligence.
Measuring Intelligence With Intelligence Tests
One of the first people to create an intelligence test was a scientist named Francis Galton. He used the biometric method, which attempted to test intelligence by using physiological measures such as the strength of a person’s grip.
However, Galton soon discovered that there was little correlation between how strong someone was and their performance on the intelligence test, which subsequently led other researchers and investigators to come up with new ways of testing intelligence.
Binet-Simon
After Galton’s work, two French scientists named Alfred Binet and Theodore Simon devised a new way to test intelligence called the Binet-Simon Scale. This intelligence test measured someone’s intelligence using the performance method, which involved testing intelligence based upon someone’s ability to give correct answers to a series of questions.
To help compare intelligences between different types of people, the Binet-Simon Scale used a measure called mental age. For example, if on average a group of nine-year olds score twenty correct questions, and then a child who is seven years old scores the same amount, then that seven-year old child is said to have a mental age of nine.
In general, mental age should rise as a person grows older. So the older they are, the better they will do on the test.
Stanford-Binet
Today, we know the Binet-Simon Scale as the Stanford-Binet Intelligence Scale, because it was translated from French into English by the Stanford psychologist Lewis Terman.
One of the things that Terman was interested in was whether children who performed well on intelligence tests did better in life than children who did poorly on the tests. To measure this, he started a longitudinal study which is a type of study that follows a group of individuals over a period of time.
After Terman’s death, his study was continued for around seventy years and the eventual results backed up what Terman had initially suspected. The study found that people with higher intelligence test scores were much more likely to be wealthier, happier and healthier than the people with lower test scores.
This result was hardly surprising however, as earlier we defined intelligence as the ability to think clearly and function effectively. Therefore, the higher a person’s level of intelligence is, the better they should do in society. It should be noted though, that this is not always true and so we must be careful not to overgeneralize Terman’s results.
A savant for example, may be extremely gifted in one particular area such as mathematics, or have extraordinary abilities such as a perfect memory, but could struggle to tie their shoelace or dress themselves. So being a genius doesn’t always guarantee that a person will be able to function effectively in society.
The Wechsler Scales
David Wechsler was a psychologist who created a series of intelligence tests known as the Wechsler Scales. These tests included:
• The Wechsler Preschool And Primary Scale Of Intelligence
• The Wechsler Intelligence Scale For Children
• Wechsler Adult Intelligence Scale
One of the major advantages of the Wechsler Scales is that unlike the Stanford-Binet test which only measured a person’s general level of intelligence, the Wechsler Scales measured different types of intelligence.
Note : The tests are called “scales” because the questions get progressively harder.
There are two types of intelligence measured by the Wechsler scale : verbal intelligence and performance intelligence. Both of these contain a number of subtests with seven subtests for verbal intelligence and six subtests for performance intelligence.
Verbal Intelligence
• Information : A person’s level of general knowledge.
• Comprehension : How well you can understand questions and grasp concepts.
• Arithmetic : A person’s mathematical abilities.
• Similarities : Measures abstract thought.
• Digit Span : Measures attention span.
• Vocabulary : How many word meanings you know.
Performance Intelligence
• Digit Symbol : Mental flexibility with random symbols.
• Picture Completion : Ability to notice differences between two similar pictures.
• Block Design : Mentally construct printed designs in your head.
• Picture Arrangement : Arrange pictures in a logical order.
• Object Assembly : Place the correct part in relationship to a whole.
IQ Score
Once a person has completed all the tests, they can then be given two separate intelligence quotient (IQ) scores: a verbal IQ score and a performance IQ score, with individual scores for each sub test within the verbal and performance categories.
Both of these scores (verbal + performance) can then be combined to give an overall IQ score.
Understanding IQ Tests
One of the problems in using mental age to measure intelligence, is that as a person’s chronological age (CA) increases so does their mental age (MA). This makes it of little value in comparing scores between different types of people because it is always rising and is therefore unstable.
In an attempt to create a more useful and stable way to measure intelligence, the German psychologist William Stern created a ratio based on the comparison of mental age and chronological age. He called this the intelligence quotient or IQ.
Note : It is called a “quotient” because the resulting score is created by division.
Calculating IQ Test Score
To calculate a person’s IQ, Stern used the following formula:
IQ = (MA/CA) x 100
For example, if a child has a CA of 10 and a MA of 10, then we can calculate their IQ with the following calculation:
10 / 10 = 1
1 x 100 = 100
IQ = 100
A score of 100 on an IQ test is regarded as an average IQ.
Above average IQ
If another child is tested who has a CA of 8 and a MA of 10, then we can calculate their IQ with the following calculation:
10 / 8 = 1.25
1.25 x 100 = 125
IQ = 125
In this IQ Test score, the child is said to have an above average IQ.
Below average IQ
If another child is tested who has a CA of 9 and a MA of 8, then we can calculate their IQ with the following calculation:
8 / 9 = 0.89
0.89 x 100 = 89
IQ = 89
In this IQ Test score, the child would be said to have a below average IQ.
Distribution Of IQ Scores
IQ is a random variable which means that IQ test scores will vary in a population according to the laws of chance. The result of this, is that IQ test scores taken from a random selection of individuals will tend to create a bell-shaped (aka Gaussian or Normal) curve.
At one end, you will have people with the lowest IQ test scores. In the middle, the people with an average IQ test score, and at the other end the people with the highest IQ test scores.
As you can see from the distribution of IQ test scores, most scores are clustered in the middle which means that most people will have an average IQ score. Fewer people will have lower IQ scores and fewer people will have higher IQ scores.
If we apply this to a population, we can generalize by saying that on average around 2% of that population will have an IQ lower than 69, 50% have an average IQ (90-109) and 2% have an IQ of 130 or above.
However, in order for any test to be produce meaningful results, it must be both valid and reliable.
Valid
A valid test is a test which measures what it is supposed to measure. So a valid intelligence test would measure intelligence and not something else like your personality. However, in order to determine the validity of a test, it is necessary to compare the scores obtained by that test with an outside criterion.
An outside criterion is a measurement instrument which is independent of the test, for example, the use of a grading marking scheme or grade point average. If an intelligence test is valid, then we would expect people with higher test scores to obtain higher grades and people with lower test scores to obtain lower grades.
The relationship between the test score and the outside criterion is determined with a correlation coefficient, which is a statistical measure of how closely two variables are related. The higher the correlation coefficient, the closer the relationship will be between intelligence scores and grades and the more reliable the test could be said to be.
Reliable
A reliable test is a test that gives the same or similar results when that test is repeated by you and by others. If a test does not produce consistent results, then the reliability of that test can be called in to question.
Types Of Tests
When measuring the validity and reliability of a test we can come to four different conclusions as to the type of test it is.
1) Neither Valid Nor Reliable
The test is not valid (i.e. it tests something it is not supposed to) and the test is not reliable (i.e. does not give repeatable results).
2) Valid But Not Reliable
The test tests what it is supposed to test, but does not give repeatable results.
3) Reliable But Not Valid
The test gives repeatable results but does not test what it is supposed to test for.
4) Valid And Reliable
The test tests what it is supposed to test for and gives repeatable results.
The Stanford-Binet Intelligence Scale and the Wechsler Scales are considered to be both valid and reliable tests of a person’s level of intelligence.
Intelligent By Nature Or Nurture?
One of the biggest questions regarding intelligence is whether it is due to heredity or the environment, something that is commonly referred to as the nature vs. nurture debate. Using these terms, nature refers to a person’s potential to reach to certain level of intelligence and nurture refers to the effect that the environment has on developing or inhibiting that intelligence.
For example, two brothers are raised by the same parents, yet later in life they have two very different careers. One is a doctor and the other is a car salesman. Since both brothers were raised in the same family, we can say that they had pretty much the same environment. As a result, the differences in intelligence between the two must be due to genetics (nature).
However, some would argue that these brothers did not have the same environment, as one child may have been given more love and attention than the other. This may then explain why one brother grew up to become more successful than the other.
This “birth-order” argument is one proposed by psychologist Alfred Adler, who believed that the environment in which we are raised as children has a big influence on our intelligence and how we develop later in life. Therefore, according to Adler, nurture is the most important factor.
Feral Children
Feral children are children who have been raised by animals or in an environment in which they received little or no human contact. One famous example of a feral child was a boy named Victor who was discovered in a French forest at age seven and subsequently studied by the physician Jean-Marc-Gaspard Itard.
Despite Itard’s efforts to teach Victor, he never did achieve a normal level of intelligence. This is something that has occurred with all feral children that have been discovered, such as the feral child “Genie” from more recent times.
Importance Of Early Childhood
What we learn from feral children is that whilst we may all have the potential to achieve a certain level of intelligence (determined by genetics/nature), it is the environment (nurture) which we are exposed to that determines whether or not we realize our innate potential.
Feral children also teach us that our early years of childhood are extremely important in developing intelligence, and that if this intelligence is not given an opportunity to develop, then after a certain period in life (i.e. a critical period, Lorenz) it may be lost completely and never develop at all. This is exactly what was found with Victor.
So in reality, it is likely that both nature and nurture are important in developing one’s intelligence. Nature (our genetics) may determine how intelligent we become, our potential intelligence, and nurture (our environment) will either allow us to reach our potential or inhibit it.
Current research tells us that children who are brought up in a stimulus rich environment where they receive lots of love and mental stimulation, are much more likely to develop higher levels of intelligence than children who are not brought up in such an environment. Feral children could be used as an extreme example of this.
Things which stimulate a child include playing with them, talking to them, exposing them to music, new toys and exposing them to printed words. Television exposure on the other hand, tends to have the opposite effect on a child as it reduces their overall level of intelligence.
Interactions
Interaction is a mathematical concept used to describe variables which affect each other in a complex way. Interactive variables are variables which when put together result in more than the sum of their parts.
For example, 4 x 4 = 16
Additive variables are variables in which the whole is a result of the sum of its parts.
For example, 4 + 4 = 8
When we apply this type of interaction to intelligence, we can see that the relationship between nature and nurture results in something “new” that is not in the original variables. In other words, nature and nurture are interactive variables because they result in something which is more than the sum of their parts.
However, we don’t know when this interaction occurs or which variable is more important (if that is the case) and when it is more important for developing intelligence.
Studies on feral children suggest that this interaction occurs very early in life and at least before age seven. So using the mathematical concept of interaction, we can say that the nature vs. nurture debate is really a false argument as both are important in developing intelligence.
We can summarize this interaction by saying :
Heredity x Environment = Intelligence
or
Nature x Nurture = IQ
Note : The “x” is used to symbolize interactive variables whose relationship results in more than the sum of its parts.
