Monday, May 25, 2009

Construct Validity

Construct validity is most directly concerned with the question of what the instrument is, in fact, measuring. What construct, concept, or trait underlies the performance or score achieved on the test ? Does the measure of attitude measure attitude or some other underlying characteristic of the individual that affects his on her score ? Construct validity lies at the very heart of scientific progress. Scientific need constructs with which to communicate. Thus, in marketing we speak of people’s sosio economic class, their personality, their attitudes, and so on. These are all constructs that we use as we try to explain marketing behavior. And although vital, They are also unobservable. We can observe behavior related to these constructs, but we cannot observe the construct themselves. Rather, we operationally define the constructs in terms of a set of observables when we agree on the operational definitions, precision in communication is advanced. Instead of saying that what is measured by these it items is the person’s brand loyalty, we can speak of the notion of brand loyalty.

Construct validity seeks agreement between a theoretical concept and a specific measuring device or procedure. For example, a researcher inventing a new IQ test might spend a great deal of time attempting to "define" intelligence in order to reach an acceptable level of construct validity.

In social science and psychometrics, construct validity refers to whether a scale measures or correlates with a theorized psychological construct (such as "fluid intelligence"). It is related to the theoretical ideas behind the personality trait under consideration; a non-existent concept in the physical sense may be suggested as a method of organising how personality can be viewed. The unobservable idea of a unidimensional easier-to-harder dimension must be "constructed" in the words of human language and graphics.

A construct is not restricted to one set of observable indicators or attributes. It is common to a number of sets of indicators. Thus, "construct validity" can be evaluated by statistical methods that show whether or not a common factor can be shown to exist underlying several measurements using different observable indicators. This view of a construct rejects the operationist past that a construct is neither more nor less than the operations used to measure it.

Construct validity is the approximate truth of the conclusion that your operationalization accurately reflects its construct. All of the other terms address this general issue in different ways. A distinction between two broad types: translation validity and criterion-related validity.

In translation validity, focus on whether the operationalization is a good reflection of the construct. This approach is definitional in nature -- it assumes you have a good detailed definition of the construct and that you can check the operationalization against it. In criterion-related validity, examine whether the operationalization behaves the way it should given your theory of the construct. This is a more relational approach to construct validity. it assumes that your operationalization should function in predictable ways in relation to other operationalizations based upon your theory of the construct.

We need to ensure, through the plans and procedures used in constructing the instrument, that we have adequately sampled the domain of the construct and that, there is internal consistency among the items of the domain. The assumption about the internal consistency of a set of items is that “if a set of items is really measuring some underlying trait or attitude, then the underlying trait cause the covariation among the items. The higher correlation, the better the items are measuring the same underlying construct”. We saw that internal consistency was also at issue in determining content validity, and as a matter of fact, negative evidence of content validity of a measure also provides negative evidence about its construct validity. A measure possessing construct validity must be internally consistent insofar as the construct is internally consistent. On the other hand, it is not true that a consistent measure is a construct validity measure. In other words, consistency is a necessary but not sufficient condition for construct validity.

Evaluation of construct validity requires examining the correlation of the measure being evaluated with variables that are known to be related to the construct purportedly measured by the instrument being evaluated or for which there are theoretical grounds for expecting it to be related. Such is consistent with the multitrait-multimethod matrix of examining construct validity described in Campbell and Fiske's landmark paper (1959). Correlations that fit the expected pattern contribute evidence of construct validity. Construct validity is a judgment based on the accumulation of correlations from numerous studies using the instrument being evaluated.

-. Marketing Research, Methodological Foundations, 5th edition, The Dryden Press International Edition, author Gilbert A. Churchill, Jr.

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