Now Criteria For Good Measurement that we have seen how to operationally define variables, it is important to make sure that the instrument that we develop to measure a particular concept is indeed accurately measuring the variable, and in fact, we are actually measuring the concept that we set out to measure. This ensures that in operationally defining perceptual and attitudinal variables, we have not overlooked some important dimensions and elements or included some irrelevant ones. The scales developed could often be imperfect and errors are prone to occur in the measurement of attitudinal variables. The use of better instruments will ensure more accuracy in results, which in turn, will enhance the scientific quality of the research. Hence, in some way, we need to assess the “goodness” of the measure developed.
What should be the characteristics of a good measurement? An intuitive answer to this question is that the tool should be an accurate indicator of what we are interested in measuring. In addition, it should be easy and efficient to use. There are three major criteria for evaluating a measurement tool:
validity, reliability, and sensitivity.
Validity is the ability of an instrument (for example measuring an attitude) to measure what it is supposed to measure. That is, when we ask a set of questions (i.e. develop a measuring instrument) with the hope that we are tapping the concept, how can we be reasonably certain that we are indeed measuring the concept we set out to do and not something else? There is no quick answer. Researchers have attempted to assess validity in different ways, including asking questions such as “Is there consensus among my colleagues that my attitude scale measures what it is supposed to measure?” and “Does my measure correlate with others’ measures of the ‘same’ concept?” and “Does the behavior expected from my measure predict the actual observed behavior?” Researchers expect the answers to provide some evidence of a measure’s validity.
What is relevant depends on the nature of the research problem and the researcher’s judgment. One way to approach this question is to organize the answer according to measure-relevant types of validity. One widely accepted classification consists of three major types of validity: (1) content validity, (2) criterion-related validity, and (3) construct validity.
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