The methods used in selection research grew out of a long psychological history ranging almost to the beginning of psychology as a scientific endeavor in Wilhelm Wundts first psychological laboratory.  Methods of understanding, evaluating and scaling individual differences were first proposed and employed by Sir Francis Galton.  It is estimated that between 1880 and 1900, Galton took over 17,000 measurements of individual differences between human subjects.  Psychophysical methods employed at about the same time by Gustav Fechner have influenced modern methods of measurement and testing theory applied in personnel selection.  For example, modern theories of Item Response Theory IRT are rooted in Fechners psychophysics.  Theories and research on individual differences form the basis for the predictive hypothesis described earlier and from which personnel selection systems are derived.  The psychological research regarding individual differences in the understanding and sensitivity to physical phenomena led to more complex theoretical discussions of differences in underlying traits such as human intelligence. 

Psychologists interested in theories of intelligence went on to develop standardized methods for assessing human intelligence.  One example of such a standardized measure is the Binet-Simon intelligence test developed in 1878.  Some of you may be familiar with the current version of this test, the Stanford-Binet.  Originally, these measures were practically used for diagnosing mental retardation in children and adult populations. But it was not long before Hugo Munsterberg, whom some have called the father of industrial psychology applied these method to measurement in service to organizations.  Munsterbergs 1913 book, Psychology and Industrial Efficiency, touches on applying psychological methods and measures to the selection of fit applicants for industrial jobs.

Further advances in personnel selection and testing were encouraged by the needs of the military, in particular the Army, in gearing up for World War I.  Robert Yerkes led a team of psychologists in efforts to place over 17,000 draftees in an appropriate assignment based upon the results of a standardized, group administered intelligence test, Army Alpha and Army Beta. 

Post World War II saw the institution of selection testing in organizational settings with many psychologists developing and validating measures of intelligence, later called cognitive ability, as well as beginning efforts to develop measures of other individual differences found to be important and critical to job success.   In particular, measures of personality based upon trait theories and/or on observations of normal and abnormal populations have been developed for various purposes, both clinical and industrial, and applied in personnel selection in order to capture more of the knowledge, skills, and abilities that underlie job success.

As time has progressed applied research in personnel selection has informed basic psychological theory and methodology, and basic theory has informed and improved methods of personnel selection.  This useful interaction between basic and applied research will continue to influence the work of I/O psychologists working to improve organizational selection decisions.