Psychometrics is the field of study (connected to psychology and statistics) concerned with the measurement of "psychological" aspects of a person such as knowledge, skills, abilities, or personality. The field of Psychometrics is primarily concerned with differences between individuals and employs statistical tools such as normal distribution and factor analysis. Measurement of these unobservable phenomena is difficult and much of the research and accumulated art of this discipline is designed to reliably define and then quantify. Critics, including "hard science" practitioners and social activists, have argued that such definition and quantification is impossibly difficult and that such measurements are very often misused (although users of psychometric techniques can reply that their critics often misuse data by not assessing them with psychometric criteria). Figures who made significant contributions to psychometrics include Karl Pearson, L. L. Thurstone, Georg Rasch and Arthur Jensen. Significant critics include the late Stephen Jay Gould.

Much of the early work in psychometrics was developed in order to measure intelligence. More recently psychometric theory has been used in measurement of personality, attitudes and beliefs, academic achievement, and in health related fields, to measure quality of life.

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For some, the field of psychometrics has controversial aspects. In part, the controversy involves the very notion of standardized tests. For others, the problematic aspects of psychometrics involve the history of the field, which involve aspects of eugenics.