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Validity is defined by Samuel Messick as an integrated, evaluative judgment of the degree to which empirical evidence and theoretical rationales support the adequacy and appropriateness of inferences and actions based on test scores or other modes of assessment. This definition opens Messick's chapter, “Validity,” in the third edition of Educational Measurement, which is a benchmark publication in the field. Although Messick's conception of validity has generated some debate, this chapter has arguably provided the dominant scholarly representation of validity in educational measurement since its publication in 1989. Like the validity chapters in the preceding (1950, 1971) and subsequent (2006) editions of Educational Measurement (by Edward E. Cureton, Lee J. Cronbach, and Michael J. Kane, respectively), it is intended to provide guidance to those who develop and use tests or other assessments, as well as philosophical grounding for validity scholars. Key elements in Messick's representation of validity, which are elaborated in the following discussion, include its tie to scientific hypothesis testing and theory building, the need to address two general threats to validity with two general types of evidence (convergent and discriminant), and the importance of attending to several aspects of validity that illuminate sets of issues and sources of evidence. Issues surrounding Messick's conception of validity include his incorporation of consequences of testing as an aspect of validity and the extent to which his representation provides sufficient guidance for practitioners. This entry also discusses current issues regarding validity.

Definitions and Scope of Application

Validation entails ascertaining the degree to which multiple lines of evidence are consonant with the intended inference (or “construct”), while establishing that alternative inferences are less well supported. This judgment takes into account the meaning of test scores as well as their relevance and utility for particular applied purposes, their value implications, and the social consequences of using them for applied decision making. Messick's definition of validity signals that validity is a property of inferences based on test scores, not tests themselves; that it is a matter of degree, not all or none; and that it evolves as new evidence is brought to bear.

He uses the term test to refer not just to tests as typically conceived but to any means of observing or documenting consistent responses, behaviors, or attributes; scores subsume qualitative and quantitative summaries of these consistencies and can refer to groups, situations, or objects, as well as persons. The term construct refers not just to unobservable qualities assumed to account for performance on a test, as originally conceived, but to whatever concept(s) the test is designed to measure. Thus, construct, score meaning, and intended inference or interpretation can be used interchangeably, as can construct validity and validity. Construct theory encompasses (a) the definition of the construct (or “construct domain”) that specifies the boundaries and facets of the construct as well as (b) the expectations (hypotheses) about responses processes, consistencies in item responses, relationships among variables, and so on.

Key Elements in Messick's Conception of Validity

The fit (or lack of fit) between the construct theory and the available evidence informs the overall judgment about the validity of the intended inference. Thus, validation incorporates all the experimental, statistical, and philosophical means by which hypotheses and scientific theories are evaluated. Messick also acknowledges the need to balance the never-ending aspect of validation with the need to make the most responsible case to guide current use of the test.

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