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            Head size & grade point averages (intelligence) studied by Francis Galton.
            Brain size & intelligence studied by Paul Broca.

•  Neither head size, brain size or sex differences have a correlation with IQ or achievement.

Binet's breakthrough in psychometrics produced the Binet-Simon Intelligence Scale which used Mental Age as a measure of intelligence.

Terman's formula for ratio IQ: Intelligence Quotient equals Mental Age divided by Chronological Age times 100.

IQ = MA / CA x 100

Today the ratio IQ has been replaced by; deviation IQ which is statistically better.

Most widely used of IQ tests:
 
•  Wechsler Adult Intelligence Scale (WAIS-III)
•  Wechsler Intelligence Scale for Children (WISC-IV)
 
•  All of the Wechsler scales are divided into six verbal & five performance subtests.
 
•  A trained examiner administers the test on a one to one basis.

Two characteristics of "good" tests; they have:
 
1. Validity - measure what they are supposed to.
    2. Reliability - they return the same results on retest.