Deviation IQ refers to an IQ obtained statistically from a person's relative standing in his or her age group, that is, how far above or below average the person's score was relative
to other scores. Deviation IQ is a method of constructing IQ scores that compares a child's performance to that of other children the same age; contrast with mental age.
Moreover, Deviation IQ is an index of intelligence derived from comparing the individual's score on an intelligence test with the mean score for that individual's reference group.
Deviation IQ is a concept introduced by Wechsler to address problems observed when applying the ratio IQ to older individuals. An individual's performance on an IQ test is compared to that of her or his age peers.