Intelligence quotient

Some tests check how we think.

These tests give us a score. This score is called an IQ.

A man named Alfred Binet helped make these tests. He wanted to help children in school. He used tasks that used words. Tests can help people find jobs. They can also help in school. Most people get a score near 100. Scores can change as people grow. It is interesting to see how we learn.

An IQ is a score from a set of tests.

These tests check how people think. They look at things like words and math.

Long ago, a man named Alfred Binet helped make these tests. He wanted to find children who needed extra help in school. He used tasks that used words. Later, Lewis Terman made a new version in the United States. This became the Stanford-Binet test. It was very popular for a long time.

Most people get a score near 100.

About two-thirds of people score between 85 and 115. Only about 2 percent score above 130.

In the past, people used these tests in bad ways. Some used them to treat people unfairly. They tried to use scores to group people by race. This was wrong and is not accepted by science today.

Tests can also show how scores change over time. Since the early 1900s, scores have gone up. This is called the Flynn effect. This means scores rise by about 3 points every ten years. Scientists still study how we learn and think.

An intelligence quotient, or IQ, is a score from a special test.

These tests help people estimate how a person thinks. They use many different tasks to measure mental ability. Some tasks use words and math. Other tasks use pictures or shapes.

Scientists use these scores to study how people learn. They also use them to help place students in the right school classes. It is important to know that IQ is just an estimate. Unlike measuring weight or distance, thinking is very abstract. This makes it hard to find one perfect measure for it.

Modern IQ tests work in a very specific way.

Most tests are designed to follow a pattern called a normal distribution. In this pattern, the average score is always 100. This means most people score near the middle. About two-thirds of all people score between 85 and 115. Only about 2 percent of people score above 130. Another 2 percent score below 70. This helps scientists see how different scores spread out across a large group of people.

Many people helped create these tests over a long time.

In 1905, Alfred Binet and Théodore Simon made the Binet–Simon test. They wanted to find children who needed extra help in school. Later, Lewis Terman at Stanford University made a new version in 1916. This became the famous Stanford–Binet scale. A man named William Stern also helped by creating the term "IQ" in 1912. In 1939, David Wechsler made a new test. His test became very popular because it used more than just word tasks.

History shows that these tests have been used in many places.

During World War I, the United States Army tested 1.75 million men. They wanted to find the best people to be officers. This was the first time tests were used on such a huge scale. However, these early tests were often not very fair. They sometimes tested if people knew American culture instead of true intelligence. Since the early 1900s, average scores have actually gone up. This rise is called the Flynn effect, and it happens by about 3 points every decade.

We must also remember that these tests have a dark history.

In the past, some people used IQ scores to be very unfair. They used them to support ideas called eugenics. This was a way to try and change human genetics by excluding certain groups. Some people used tests to justify racism or to push for laws that hurt others. Mainstream science has rejected these ideas completely. Today, we know that many things like nutrition and environment affect how people score. We study these connections to better understand how everyone grows and learns.

An intelligence quotient, or IQ, is a numerical score derived from standardized tests. These tests use various subtests to assess human intelligence. While we often think of intelligence as a single thing, it is actually an abstract concept. Because it is abstract, we cannot measure it like we measure mass or distance. Instead, an IQ score serves as an estimate of mental ability.

Researchers use these scores to study populations and predict things like job performance or income. They also help with educational placement for students.

Modern IQ scoring follows a specific mathematical pattern called a normal distribution. In this system, the mean, or average, is set at 100. The standard deviation, which measures how scores spread out, is 15. This structure means most people score near the middle. Specifically, about two-thirds of the population scores between 85 and 115. The extremes are much rarer. Only about 2 percent of people score above 130, and another 2 percent score below 70.

The history of these tests began with early attempts to classify human behavior. In 1882, Francis Galton set up the first mental testing center. He was a pioneer of psychometrics, which is the use of statistical methods to study human traits. Galton believed intelligence was largely a product of heredity. He tried to find correlations between intelligence and physical traits like head size or muscle grip. However, he could not prove these links and eventually abandoned his research.

In 1905, Alfred Binet and Théodore Simon developed a more successful method. They created the Binet–Simon Intelligence test to focus on verbal abilities. Their goal was to identify children who needed extra help in school. They wanted to distinguish these children from those who were actually sick. The test could reveal a child's mental age. For example, a six-year-old who performed tasks typical of a six-year-old had a mental age of 6.0.

Later, Lewis Terman revised this into the Stanford–Binet scale in 1916. The term "IQ" itself was coined by William Stern in 1912.

Psychologists have debated what exactly these tests are measuring. In 1904, Charles Spearman proposed the idea of a "g factor." This stands for a general intelligence factor. Spearman noticed that children's grades in different subjects were often related. He reasoned that an underlying general mental ability influenced all mental tests. He called this "g" and labeled specific task abilities as "s."

Other researchers, like L.L. Thurstone, argued for a different model. He suggested intelligence included seven different factors, such as verbal comprehension and spatial visualization.

IQ testing saw massive expansion during World War I. The United States Army needed to assign recruits to specific tasks. Robert Yerkes worked with other psychologists to develop these tests. A total of 1.75 million men were tested during this time. This was the first time intelligence tests were mass-produced. The results helped screen men for officer training. In some camps, no man scoring below a "C" could become an officer. However, these tests were controversial. Many believed they tested familiarity with American culture rather than actual intelligence.

We must also acknowledge the dark history involving the eugenics movement. Eugenics is the belief in improving human genetics by excluding certain groups. This movement was rooted in the ideas of Francis Galton. Some psychologists, like Henry Goddard, used IQ tests to support eugenicist goals. Goddard used the term "feeble-minded" for low scorers. He argued that this was caused by heredity. This led to the promotion of forced sterilization laws. In the United States, these laws resulted in over 60,000 people being sterilized.

Mainstream science has since rejected these racist and pseudoscientific ideas.

Today, we understand that many factors influence IQ scores. These include nutrition, parental socioeconomic status, and the perinatal environment. We also see a phenomenon called the Flynn effect. This describes how raw IQ scores have risen by about three points per decade since the early 20th century. Modern tests, like the Wechsler scale, attempt to be more comprehensive. The Wechsler test became popular because it includes both verbal and nonverbal abilities.

This allows for a broader view of human intelligence than older models.