Understanding Psychology (10th Ed)

288 Chapter 
9 
Intelligence
dull groups, and—with further work—one that distinguished among children in differ-
ent age groups (Binet & Simon, 1916; Sternberg & Jarvin, 2003). 
On the basis of the Binet test, children were assigned a score relating to their 
 mental age,  the age for which a given level of performance is average or typical. For 
example, if the average 8-year-old answered, say, 45 items correctly on a test, anyone 
who answered 45 items correctly would be assigned a mental age of 8 years. Conse-
quently, whether the person taking the test was 20 years old or 5 years old, he or 
she would have the same mental age of 8 years (Cornell, 2006).
Assigning a mental age to students provided an indication of their general level of 
performance. However, it did not allow for adequate comparisons among people of 
different chronological ages. By using mental age alone, for instance, we might assume 
that an 18-year-old responding at a 20-year-old’s level would be demonstrating the same 
degree of intelligence as a 5-year-old answering at a 7-year-old’s level, when actually 
the 5-year-old would be displaying a much greater relative degree of intelligence. 
A solution to the problem came in the form of the  intelligence  quotient,   (IQ), 
a score that takes into account an individual’s mental and chronological ages. His-
torically, the fi rst IQ scores employed the following formula in which MA stands for 
mental age and CA for chronological age:
IQ score 
5
MA 
3
100
CA
Using this formula, we can return to the earlier example of an 18-year-old per-
forming at a mental age of 20 and calculate an IQ score of (20/18) 
3
100 
5
111. In 
contrast, the 5-year-old performing at a mental age of 7 comes out with a consider-
ably higher IQ score: (7/5) 
3
100 
5
140.