Early Roots of Psychometrics Before Francis Galton

Although one of the flagships of psychometrics, factor analysis, could not have been invented without Francis Galton’s (1822–1911) groundbreaking concept of correlation, some other psychometric concepts had been explored already before his time. Christian Thomasius (1655−1728) pioneered personality assessment using numerical rating scales and introduced a first notion of psychometric reliability. It was Christian Wolff (1679−1754) who coined the term “psychometria” and who identified the basic difficulty of finding a suitable unit for measurement of psychological variables. Halfway the nineteenth century, Gustav Fechner (1801–1887) not only founded psychophysics but also introduced before Galton the statistical approach to the analysis of psychological data—which is so typical for psychometrics in general. He also developed some pathbreaking experimental designs for data collection, as well as the notions of a psychological scale and the psychometric function.