An IQ test is a test of cognitive skills that produces an IQ score. This refers to an intelligence quotient, which is an estimate of general intelligence. IQ tests have multiple subtests to tap different kinds of intellectual skills, such as memory, vocabulary, reasoning, attention, and copying skills. Tests therefore can include lists of vocabulary words to define, arithmetic problems, or drawings to be copied. All subtests have both easy and hard items, and the items become more difficult as the test goes on. The score is based on the number of items answered correctly.

Test norms allow comparison of any individual’s score with those of the general population. In other words, when a test is normed, it is possible to know the percentile rank of any given score, which means the percentage of people who scored below it. In order to establish test norms, the test is administered to a large sample of people. The average (or mean) score and the standard deviation are then calculated. The standard deviation measures how much the individual scores vary from the average score. Are all the scores clustered tightly around the mean or are they all spread out? If you know both the mean and the standard deviation of a test, you can determine the percentile rank of any score. Thus IQ scores reflect a person’s percentile rank according to the tests’ norms.