Imagine that you were to test a variable of your own design measuring ideology for validity. What tests might you use, how would each test confirm validity, and what problems might you encounter in establishing validity?

Question

What will be an ideal response?

Answer 1

Essentially, a valid measure is one that measures what it is supposed to measure. Unlike reliability, which depends on whether repeated applications of the same or equivalent measures yield the same result, validity refers to the degree of correspondence between the measure and the concept it is thought to measure. A measure’s validity is more difficult to demonstrate empirically than is its reliability because validity involves the relationship between the measurement of a concept and the actual presence or amount of the concept itself. Information regarding the correspondence is seldom abundant. Nonetheless, there are ways of evaluating the validity of any particular measure. Face validity may be asserted (not empirically demonstrated) when the measurement instrument appears to measure the concept it is supposed to measure. To assess the face validity of a measure, we need to know the meaning of the concept being measured and whether the information being collected is “germane to that concept.” Content validity is similar to face validity but involves determining the full domain or meaning of a particular concept and then making sure that measures of all portions of this domain are included in the measurement technique. A third way to evaluate the validity of a measure is by empirically demonstrating construct validity. When a measure of a concept is related to a measure of another concept with which the original concept is thought to be related, convergent construct validity is demonstrated. In other words, a researcher may specify, on theoretical grounds, that two concepts ought to be related in a positive manner (say, political efficacy with political participation, or education with income) or a negative manner (say, democracy and human rights abuses). The researcher then develops a measure of each of the concepts and examines the relationship between them. If the measures are positively or negatively correlated, then one measure has convergent validity for the other measure. Discriminant validity involves two measures which theoretically are expected not to be related and thus the correlation between them is expected to be low or weak. If the measures do not correlate with one another, then discriminate construct validity is demonstrated. A fourth way to demonstrate validity is through interitem association. This is the type of validity test most often used by political scientists. It relies on the similarity of outcomes of more than one measure of a concept to demonstrate the validity of the entire measurement scheme. It is often preferable to use more than one item to measure a concept?reliance on just one measure is more prone to error or misclassification of a case. Validity of the measures used by political scientists is seldom demonstrated to everyone’s satisfaction. Most measures of political phenomena are neither completely invalid nor valid but, rather, are partially accurate. Therefore, researchers generally present the rationale and evidence available in support of their measures and attempt to persuade their audience that their measures are at least as accurate as alternative measures would be. Nonetheless, a skeptical stance on the part of the reader toward the validity of political science measures is often warranted.