“Psychometrics” refers to the scientific discipline that combines psychological inquiry with quantitative measurement. Though psychometric theory and practice pertain to all aspects of measurement, in the current context, psychometric approaches to expertise pertain to the measurement and prediction of individual differences and group differences (e.g., by gender, age) and, in particular, high levels of proficiency including expertise and expert performance. The scientific study of expertise involves several important psychometric considerations, such as reliability and validity of measurements, both at the level of predictors (e.g., in terms of developing aptitude measures that can predict which individuals will develop expert levels of performance), and at the level of criteria (the performance measures themselves). We will discuss these basic aspects of psychometric theory first, and then we will provide an illustration of psychometric studies that focus on the prediction of expert performance in the context of tasks that involve the development and expression of perceptual-motor skills, and tasks that involve predominantly cognitive/intellectual expertise. Finally, we will discuss challenges for future investigations.

Before we start, some psychological terms need to be defined. The first terms are “traits” and “states.” Traits refer to relatively broad and stable dispositions. Traits can be physical (e.g., visual acuity, strength) or psychological (e.g., personality, interests, intelligence). In contrast to traits, states represent temporary characteristics (e.g., sleepy, alert, angry). The second set of terms to be defined are “interindividual differences” and “intraindividual differences.”