Mental age

Mental age is a controversial concept in psychometrics. It is an intelligence test score, expressed as the chronological age for which a given level of performance is average or typical.

How mental age is used to derive an IQ score
After taking a standardized test, an individual's mental age is divided by his chronological age and multiplied by 100, yielding an intelligence quotient (IQ). Thus, a subject whose mental and chronological ages are identical has an IQ of 100, or average intelligence.

Louis Leon Thurstone was among prominent critics, stating "The Mental Age concept is a failure in that it leads to ambiguities and inconsistencies." This criticism however mainly focused on the use of mental age concept for adults. Mental age is nowadays used for monitoring children's educational progress and is seldom expressed as an IQ score.

Mental age in video games
In the Nintendo DS video game Brain Age, the player completes different activities using the DS's features, like the microphone, to find their mental age, from 20-80.