The concept of Intelligence Quotient (IQ) does not really have an exact and universal definition, although most experts agree that IQ tests can evaluate a person's ability to use learned knowledge and process new information. This means that IQ tests differ when testing these characteristics in a person. For example, the WISC tests verbal, perceptual, memory, processing speed and executive function, while KABC-II offers tests related to simultaneous thinking, sequential processes, planning, general learning and stock knowledge.
IQ Tests not only differ in coverage, but they also target different areas of intelligence to get the best possible estimate of a person's IQ. Developers of IQ tests aim to make their tests as accurate as possible by creating different strategies on how to formulate questions, considering the social backgrounds of the general public, and testing the whole test with control group to produce an average score. IQ tests have varying score interpretations because they use different ways to formulate and standardize these scores.
Another reason why IQ tests are different is because people have multiple and different types of intelligences. Some people are more cognitive than others, meaning one person might be able to solve mathematical problems easily, but might have problems answering language questions. IQ tests greatly differ in the number of questions they produce for each type of intelligence, and often have different preferences on what type of intelligence can be tested accurately. For example, musical intelligence cannot be tested as easily and accurately as logic-based intelligence.
Just like any other tests, IQ tests also need to be different from each other based on the people that will take them. Children have a different IQ test than adults, with some IQ tests having different brackets depending on the age and physical capability of the person testing. The KABC-II IQ test is designed for people who are between 3 and 18 years old, while the WAIS-III is designed for 16 to 89 year olds. Tests might also be divided into cultural groups, as certain cultural groups will have a slightly skewed set of knowledge as compared to others.