The Story of Psychology (42 page)

After pondering the matter for a long while, Galton set down a “scatter plot” of the heights of some three hundred children. First he created a grid, the horizontal dimension of which was children’s heights and the vertical dimension of which was parents’ heights (actually, the heights of “mid-parents”—the average of each parental pair). Then, in each cell of the grid (each intersection of a particular children’s height and a particular parental height) he wrote down the number of children who fit that category. The scatter plot looked like this:

For a time, it revealed nothing to him; then one morning, poring over it while waiting for a train, he suddenly saw a regularity in the numbers. If he drew a line connecting any set of approximately equal values, it would describe a tipped-over ellipse whose center point was the midpoint of the scatter plot (the averages for both parents and children). When he did so and then drew lines across the ellipse connecting its extreme horizontal and vertical points, they passed through the average height of children in each vertical column and the average height of parents in each horizontal row. It looked like this:

The ellipse and the lines crossing it revealed the relationship he had been looking for. At any given parental height (“Locus of horizontal tangential points”), the average height of the children was only about two-thirds as far from the mean (average) as that of the parents; that is, the children had “regressed” a third of the way toward the mean.
¹⁴
Conversely, for any children’s height (“Locus of vertical tangential points”), parents were somewhat closer to the mean (that is, parents of unusual children were less unusual than their children).

Galton had discovered the analytical device of the “regression line.” If the children’s heights had been exactly the same as the parents’, the two regression lines would have coincided; if the children’s heights had no relation whatever to the parents’, the regression lines would have been perpendicular to each other. As it was, they were fairly close, meaning that the relation between the two variables in this case—their
correlation—
was about midway between total and nil.

That was in 1886. Ten years later the British biometrician Karl Pearson, a Galton disciple and later his biographer, worked out a mathematical means of calculating the “coefficient of correlation”—which he called
r
, for regression—without any need to create scatter plots. For any two sets of data, it would show a correlation ranging from 1 (a perfect one-to-one covariation) to 0 (no relationship whatever) and to −1 (a totally inverse relationship). The Pearsonian method has been the standard way of evaluating correlation to this day. In the case of parents and
children,
r
turned out to be .47 (somewhat different from Galton’s first calculations): that is, children averaged about half as far from the population’s average as their parents.
¹⁵

The importance of Galton’s discovery of correlation analysis can hardly be overestimated. It meant that whenever two variables change in the same direction (or the opposite direction), even though not to the same degree, they are correlated, and the strength of the correlation indicates how meaningful the relationship between them is. The stronger the relationship, the less likely it is happenstance and the more likely the connection is causal. One variable may be the cause (or a contributing cause) of the other, or vice versa, or they may be the concurrent and linked effects of some other cause. In either case, a strong correlation suggests an explanation of the phenomenon under study. In the numbers are, if not answers, at least clues.

(Even a strong correlation, to be sure, may be “spurious”—an artificial result of some other cause. In men, for instance, the degree of baldness correlates with length of marriage—not because one has any connection with the other but because age is related to each. Later techniques of analysis have been able to screen out such misleading correlations.)

The psychologist George Miller, appraising the value of Galton’s discovery, writes:

Add to that his many other important methodological contributions and one can see why, although Galton was not a profound thinker, Raymond Fancher says that “few men have had greater impact on modern psychology.”
¹⁷

The outcome of Galton’s work is a paradox. Although several of his methodological inventions are of vital importance in contemporary psychological
research, his name means little to most psychologists and is all but unknown to the public. Working alone outside a university setting, he created no school of psychology, supervised no doctoral dissertations, and had few followers. Moreover, his chief contributions were research methods rather than illuminating theories, but the world remembers the latter, even though ingenious research methods are often the route to great insights.

And there is another and larger paradox. The measuring of individual differences in intelligence, a prominent goal of Galton’s life, has had a great impact on Western society since the early part of the present century—but not by means of his method. Although he conceived of and originated mental testing, his name is not linked with any of the tests used today or in the past ninety years; except in histories of psychology, he is remembered, if at all, as the originator not of mental testing but of eugenics.

In Great Britain, Galton was the founder of a “new psychology” of individual differences, but almost no British psychologists thought of themselves as Galtonians.
¹⁸
In the latter part of the nineteenth century most British experimental psychologists went to Germany for training and brought Wundtian procedures and theory back with them. They adopted many of Galton’s ideas and methodological inventions but considered themselves Wundtians. The new German psychology was held in much greater esteem than the British; it was the product of the university system and was “pure,” while Galton’s was the product of a gifted amateur and was intended to serve practical purposes.

Galton’s effect was greatest in America, but again not in the form of a school of psychology. Before the turn of the century, many American psychologists were structuralists (Wundtians), who had no interest in the measurement of individual differences. By 1905 the functionalists (Jamesians) were dominant, but though they were sympathetic to many of Galton’s ideas, they defined themselves in grander theoretical terms than those of his psychology. Like William James, many leading figures in American psychology, including John Dewey, James Rowland Angell, George H. Mead, James McKeen Cattell, Edward Lee Thorndike, and Robert S. Woodworth, based their theories on the evolutionary selection of the mentally fittest and its social equivalent, the struggle to get ahead. None called himself a Galtonian, but they shared a utilitarian outlook and all of them, therefore, valued Galton’s methods of measuring individual differences because the methods were so practical.
¹⁹

The most enthusiastic advocate of anthropometric measurement was James McKeen Cattell (1860–1944).
²⁰
Born in Easton, Pennsylvania, and educated there at Lafayette College, he went to Leipzig in 1883 and studied with Wundt until 1886. His main research interest was the study of reaction times, but he was a fiercely independent young man and dared to differ with the great Wundt on a key methodological issue: Cat-tell doubted that anyone could really introspect in the manner called for by Wundt, namely, by subdividing reaction time into perception, choice, and so on. As a consequence, Cattell, though he was Wundt’s laboratory assistant, had to carry out some of his work in his own quarters, because Wundt would not allow in the laboratory research by those who could not or would not follow his introspection method.

Cattell was intrigued by the differences in reaction time among the people he tested, and discussed it as a matter of “special interest” in an 1885 paper.
²¹
After earning his doctorate the following year, he went to London, met Galton, and, despite nearly a forty-year gap in their ages, found him a kindred spirit. Deeply impressed by Galton—many years later Cattell called him “the greatest man whom I have known”—he worked for him off and on for two years in the Anthropometric Laboratory at the South Kensington Museum and became thoroughly conversant with the tests performed there.

In 1888, at only twenty-eight, Cattell became a professor of psychology at the University of Pennsylvania (probably the first person in the world to hold that title; James, at Harvard, was not designated a professor of psychology until the following year). Cattell assembled a set of fifty tests, some Galtonian and some adapted from Fechner, Wundt, and other sources, and administered ten of them to his students to measure individual differences in intelligence. He supposed, as Galton had, that the chiefly physical characteristics measured by the tests were related to intelligence: strength of grip, speed of arm movement, reaction time to sound, just noticeable differences in weight, memory span for letters, and five others. In 1890, he described his work in a paper, in the journal
Mind
, called, “Mental Tests and Measurements”; it was the first use of that term and launched the mental-testing movement.

In 1891 Cattell moved to Columbia University as professor of psychology and head of the department. He expanded his battery of tests and each year gave them to fifty volunteers from among the entering freshmen. His admirable aim was to prove that the tests measured intelligence by showing a relationship between the test results and the students’
grades; toward that end, he collected test data and student grades for close to a decade. Meanwhile the same method of testing intelligence was demonstrated at the Chicago World’s Fair of 1893, where Joseph Jastrow, a leader of the American Psychological Association, created a virtual replica of Galton’s Anthropometric Laboratory. Visiting psychologists undoubtedly found it interesting and impressive; during the 1890s such testing was begun in a number of laboratories in America and Europe.

By 1901 Cattell had collected enough data for a definitive study, and Clark Wissler, one of his students, performed a Galton-Pearson correlation analysis of them. His findings astonished and dismayed Cattell: there were no significant correlations between the students’ grades and any of the anthropometric tests. If grades and academic standing were indications of intellectual ability, the anthropometric tests were not.
²²
Furthermore, the tests were so little correlated with one another that it seemed plain they were not measuring a common attribute, as intelligence was presumed to be. Thus by yet another paradox, it was Galton’s discovery, correlation analysis, that invalidated his own method of intelligence testing.

But that was not the end of the story for Cattell or for mental testing. Cattell, undaunted, developed a number of other tests, particularly in the field of value judgments, edited two science magazines, founded the Psychological Corporation to do applied psychology as a business, and became the prime exemplar of the hustling, practical, commercial side of psychology.

Although Galton’s anthropometric approach to mental testing died out rapidly, intelligence testing of a different sort shortly took its place and soon made the study of individual differences the leading area of American psychology. By 1917, well over half of all research reported at meetings of the American Psychological Association dealt with individual differences.
²³
Galton’s assessment of the value of mental testing came to dominate American psychology, and intelligence testing became the means by which his hereditarian views influenced the schooling offered to students, the assignments given men in the military service, and the immigration policies of the nation.