An intelligence quotient (IQ) is a relative index produced by converting a score on a standardized intelligence test against the distribution of a same-age reference population. Most instruments are scaled to a mean of 100 and a standard deviation of 15, so an IQ of 115 sits one standard deviation above the mean - roughly the top 16 percent. It is not an absolute quantity of ability but a statement of position within a reference group, which means the same person's number moves when the reference group changes.
How the Score Is Derived and Why Standardization Matters
The intelligence quotient in common use is calculated as a deviation IQ. Age-banded score distributions are obtained from large reference samples, and an individual's score is converted by locating it within them. That conversion presupposes that the test is administered under uniform conditions. The examiner's qualifications, the wording read aloud, how time limits are measured, even the state of the room are specified strictly, because if conditions drift then scores drift and the premise behind the conversion collapses. Standardization is precisely the work of securing that comparability.
Limits of Interpretation
An intelligence quotient is a composite of several subtests, and when the profile across facets such as verbal comprehension, perceptual reasoning, working memory, and processing speed differs, two identical numbers can sit on different patterns of strength and weakness. The ability to read a social situation, persistence, and creativity fall outside what the battery examines at all. Viewed statistically across a population the measure correlates with outcomes such as academic attainment, but a correlation is not a formula that fixes an individual's future. Results and income vary among people with the same number, and learning environment, health, and access to opportunity are among the factors involved in that spread.
Distinguishing Quick Tests on the Web
Most of the 'IQ tests' available in a browser have not been standardized. They hold no age-banded reference sample, impose no consistency on the testing environment, and do not track the number of retakes. Even when the question format resembles that of a genuine instrument, the number produced is not an intelligence quotient. A meta-analysis of studies in which applicants in selection settings retook cognitive ability tests found that scores rose on retest, with larger gains when identical forms were used. Standardized instruments control the interval between retests, whereas a test on the web carries no such constraint.