Psychometrics

For information regarding the parapsychology phenomenon of distance knowledge, see psychometry.

Definition of measurement in the social sciences

The definition of measurement in the social sciences has been a controversial issue. A currently widespread definition, proposed by Stanley Smith Stevens (1946), is that measurement is "the assignment of numerals to objects or events according to some rule". This definition was introduced in the paper in which Stevens proposed four levels of measurement. Although widely adopted, this definition differs in important respects from the more classical definition of measurement adopted throughout the physical sciences, which is that measurement is the numerical estimation and expression of the magnitude of one quantity relative to another (Michell, 1997). Indeed, Stevens' definition of measurement was put forward in response to the British Ferguson Committee, whose chair A. Ferguson was a physicist. The committee was appointed in 1932 by the British Association for the Advancement of Science to investigate the possibility of quantitatively estimating sensory events. Although its chair and other members were physicists, the committee also comprised several psychologists. The committee's report highlighted the importance of the definition of measurement. While Stevens' response was to propose a new definition, which has had considerable influence in the field, this was by no means the only response to the report. Another, notably different, response was to accept the classical definition, as reflected in the following statement:

Related Topics:
Stanley Smith Stevens - Levels of measurement

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:Measurement in psychology and physics are in no sense different. Physicists can measure when they can find the operations by which they may meet the necessary criteria; psychologists have but to do the same. They need not worry about the mysterious differences between the meaning of measurement in the two sciences (Reese, 1943, p. 49).

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These divergent responses are reflected to a large extent within alternative approaches to measurement. For example, methods based on covariance matrices are typically employed on the premise that numbers, such as raw scores derived from assessments, are measurements. Such approaches implicitly entail Stevens' definition of measurement, which requires only that numbers are assigned according to some rule. The main research task, then, is generally considered to be the discovery of associations between scores, and of factors posited to underlie such associations. On the other hand, when measurement models such as the Rasch model are employed, numbers are not assigned based on a rule. Instead, in keeping with Reese's statement above, specific criteria for measurement are stated, and the objective is to construct procedures or operations that provide data which meet the relevant criteria. Measurements are estimated based on the models, and tests are conducted to ascertain whether it has been possible to meet the relevant criteria.

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