What makes IQ tests reliable

If you google the word "IQ test" today, you get more than seven million hits in a fraction of a second: "Free IQ test: Are you gifted?" - such search results can be found in abundance. Hence, it is not surprising that IQ tests have their critics. Even some layperson doubts the meaning and validity of such a large number of different tests.

In fact, there is still no uniform definition of what is meant by intelligence. "Intelligence is what the intelligence test measures," claimed the American psychologist Edwin Boring as early as 1923. And whether intelligence can be measured at all - that is, the intellectual power or the cognitive performance of a person - opinions have been divided on this question for more than 100 years.

As early as 1904, the Frenchman Alfred Binet laid the foundation for today's tests. Together with his colleague Théophile Simon, Binet put together five questions for each age group of French schoolchildren, with which he wanted to find out whether a child was ahead of its peers in its intellectual development or was lagging behind them.

The psychologists tried to measure the "intelligence age" (IA). For example, if eight-year-old students were even able to solve the tasks for nine-year-olds, they had a higher IA than those who could only answer the questions corresponding to their age.

For many experts, however, Binet's test was insufficiently informative. The German psychologist Wilhelm Stern therefore developed the unit of measurement of the intelligence quotient, which is still in use today, about ten years later. Stern divided the "intelligence age" by the age and multiplied the result by a hundred. The IQ was born.

But the sense of every IQ test, it soon became clear to the scientists, stands or falls with the questions asked, and they depend on the questioner. In the 1960s, the British-American psychologist Raymond Bernhard Cattell assumed a fluid, innate intelligence and a crystalline intelligence based on learned skills.

20 years later, the US psychologist Howard Gardner was already speaking of multiple intelligence: among other things, musical, logical-mathematical, linguistic, personal and motor intelligence. And Theodor Adorno criticized early on that only those behaviors are described as intelligent that are appropriate to the "most advanced level of technical development" - even where this is not necessary at all.

The large number of different IQ tests is therefore no wonder. They are based on different intelligence models. Therefore one cannot speak of "the IQ" either. And for each individual, the results will vary from test to test.

But that does not speak against the usefulness of the tests, as Franzis Preckel from the University of Trier emphasizes. "I don't see any defects in the tests themselves. These are just different methods. Choosing between them is like choosing between a pencil or a ballpoint pen," explains the psychologist.

"The person using the test is responsible for choosing the best possible practice." Therefore, the necessary specialist knowledge as well as a completed psychology degree are also a basic requirement in order to adequately carry out such tests.

You can't reduce people to a number

Attention must be paid to the measurement accuracy of the process as well as to its theoretical foundation. And ultimately it is also important to know which statements the test result allows and which not. "If someone says that a person with an IQ of 123 is more intelligent than someone with an IQ of 120, that is of course nonsense," says Preckel.

"You can't just reduce people to a number," explains the psychologist. "But if you embed the results in a person's life context, then intelligence tests are indispensable."

An example of an important area of ​​application for intelligence tests is personnel selection. With IQ tests, applicants' cognitive abilities can be assessed and positions can be filled better right from the start. Then there were also no costs for any follow-up training in the event that employees fail to perform as expected.

"The tests cannot only be used by employers who are looking for the best," explains Preckel. "The employee also wants to find a job where he can develop optimally. Ultimately, this also promotes subjective well-being."