144 PSYCHOLOGY
MA stands for mental age.
CA stands for chronological ageCA is divided into MA and multiplied by 100. Stern suggested the multiplication
step be employed with the aim of getting rid of decimals in the final quotient. For
example, instead of an IQ being reported as 1.15, it is reported as 115.
Let’s say that Irwin has a CA of 9 and an MA of 9; 9 ÷ 9 =1. Multiply 1 by
100 and the product is 100. Consequently Irwin’s IQ score is 100. This is a nor-
mal, or average, IQ. This makes sense in view of the fact that the average child of
9 years old will also have a mental age of 9. Let’s say Irwin is tested again when he
is 11 years old. His MA is now 11. A CA of 11 divided into an MA of 11 is 1. So
Irwin’s IQ is still 100.
Let’s say that Lana has a CA of 8 and an MA of 10; 10 ÷ 8 =1.25. Multiply by
100 and Lana’s IQ score is 125, above normal.
Let’s say that Jeffrey has a CA of 9 and an MA of 8; 8 ÷ 9 =.89. Multiply by
100 and Jeffrey’s IQ score is 89, below normal.(a) Stern suggested that a based on the comparison of mental age with
chronological age would tend to be relatively.(b) What is the formula for IQ?
Answers: (a) ratio; stable; (b) IQ =M
CAA×100.Research has demonstrated that the IQ score is a random variable, meaning a
variable distributed according to the laws of chance. This means that in a large
sample of scores the scores will tend to take on a bell-shaped distribution. This
distribution, well studied by statisticians, goes by three names: (1) the bell-shaped
curve,(2) the normal curve,and (3) the Gaussian curve.The third name is in
honor of the nineteenth-century German mathematician Karl Friedrich Gauss,
who first studied the curve’s properties. Applying the curve to IQ scores, seven
categories emerge. These are summarized in the accompanying table.70 80 90 100 110 120 130 IQ scores
A large sample of IQ scores tends to display a bell-shaped distribution.