When we want to determine how intelligent a person is, our aim is to examine how their mental actions work. We want to see how they acquire the knowledge that helps them complete tasks by using thought, their experiences, and by using their senses. 

How Intelligence Tests Work

Alfred Binet and Theodore Simon developed a series of sliding scales to define intelligence in the early 1900s. With the world at war between 1914 and 1918, Alpha and Beta intelligence tests were also used to examine the literacy of the men sent to fight. Those who could read were then given different duties from those who couldn’t. 

Another pioneer in testing was an American, David Wechsler. His IQ test scales were first developed in the 1930s with designs that drew off of Binet and Simon’s, but he also included the subject’s age in calculations. Thanks to this adaptation, it became apparent that a person’s IQ remains the same throughout their life. 

Development of the Intelligence Quotient (IQ)

The Intelligence Quotient, which is most commonly known by just its initials IQ, is a description of intelligence presented as a number.

If one scores more than 100 on their test then they’re more intelligent than average. On the flip side, if they score less than 100, they’re less intelligent than average. 

There’s also a margin based on something called the standard deviation. If the average score of the test is 100 points with what’s called a standard deviation of 15 points, then that means that approximately seven out of ten of the people your age who took the test will score either 15 points less or 15 points more than the average.

Increasing the standard deviation to 30 points, meaning an interval of results from 70 to 130, also has implications. It means that more than nine out of ten people - approximately 97.5% - who took the test are placed within 30 points less or 30 points more than the average score. 

If your score was 130, only 2.5% of your peers would be more intelligent than you.