Francis Galton as Differential Psychologist:
Galton
was one of the first experimental psychologists, and the founder of the field of
enquiry now called Differential Psychology, which concerns itself with
psychological differences between people, rather than on common traits. He
started virtually from scratch, and had to invent the major tools he required,
right down to the statistical methods - correlation and regression - which he
later developed. These are now the nuts-and-bolts of the empirical human
sciences, but were unknown in his time. One of the principal obstacles he
had to overcome was the treatment of differences on measures as measurement
error, rather than as natural variability.
His influential study
Hereditary Genius (1869) was the first systematic attempt to investigate
the effect of heredity on intellectual abilities, and was notable for its use of
the bell-shaped Normal Distribution, then called the "Law of Errors", to
describe differences in intellectual ability, and its use of pedigree analysis
to determine hereditary effects.
Later Galton went on to suggest the use of twin studies to disentangle nature
from nurture, by comparing identical twins to fraternal twins. The
research program that Galton initiated in this regard has developed into the
important field of behaviour genetics.
Galton later broadened his study of human traits into general
anthropometry, or "measurement of man",
trying to find as many measurable traits as possible, so that their distribution
and heritability could be determined.
His psychological studies also embraced mental differences in visualization,
and he was the first to identify and study "number forms", now called "synaesthesia".
He also invented the word-association test, and investigated the operations of
the sub-conscious mind. His work in this area was collected into a
wide-ranging volume called Inquiries
into Human Faculty, which must be read today with Galton's broader
research program in mind: to identify and measure variable human traits.
Inheritance of ability
General Psychology
Psychometrics