Types of validity in research: content validity

In psychometric terms, validity is a concept that has gone through a long evolutionary process. At the beginning, Muniz (1996) works the validity with a specific position.

In statistical terms, validity is defined as the true proportion of the variance that is relevant to the test penalties. With the term 'relevant' we refer to what is attributable to the variable, the characteristics that the test measures. But, do we know that there are several types of validity?

In this sense, generally the validity of a test is defined either by means of:

●      The relationship between its proportions with some measure of external criteria, or,

●      The extent to which the test measures a hypothesized specific underlying trait or “construct”.

Validity in psychometric terms

In psychometric terms, validity is a concept that has gone through a long evolutionary process. At the beginning, Muñiz (1996) worked the validity with a specific position. This held that "a test is valid for that with which it correlates."

Now, validity is understood as a global evaluative judgment. In this judgment, the empirical evidence and the theoretical assumptions support the sufficiency and appropriateness of the interpretations not only of the items, but also of the way people respond as well as the context of the evaluation.

So what is validated is not the proof. What is validated in particular are the inferences made from it. This has two consequences:

●      The person responsible for the validity of a test is no longer only its constructor, but also the user.

●      The validity of a test is not established once and for all. It is the result of the collection of evidence and theoretical assumptions that occur in an evolutionary and continuous process. This includes all the experimental, statistical and philosophical questions through which scientific hypotheses and theories are evaluated.

In this context, the concept of validity refers to the appropriateness, meaning, and usefulness of specific inferences made from test scores. Test validation is the process of accumulating evidence to support such inferences. Thus, validity is a unitary process. Although evidence can be accumulated in many ways, validity always refers to the degree to which that evidence supports the inferences made from the scores.

Types of evidence

In 1954, a committee chaired by L. J. Cronbach established on behalf of the American Psychological Association (APA) that validity was of four types. These are:

●      Content validity.

●      predictive validity.

●      concurrent validity.

●      Construct validity.

Currently, it is agreed, from a scientific point of view, that the only admissible validity is construct validity (Messick, 1995).

Validity and its aspects

Within the study of validity, the evidence is related to five aspects:

●      The content (the relevance and representativeness of the test).

●      The noun (the theoretical reasons for the observed consistency of the responses).

●      Structural (internal configuration of the test and dimensionality).

●      Generalization (the degree to which inferences made from the test can be generalized to other populations, situations, or tasks).

●      External (relationships of the test with other tests and constructs).

●      Consequence (ethical and social consequences of the test).

Thus, within this validity we can understand other types of validity or strategies. As we have previously mentioned, these are content validity, predictive validity, concurrent validity, and construct validity.

Types of validity: content validity

In this type of validity, the following question is answered. Are the items that make up the test really a representative sample of the content domain or behavioral domain that interests us?

So that we understand each other, a behavioral domain or field is a hypothetical grouping of all possible items that cover a particular psychological area. For example, a vocabulary test should be an adequate sample of possible item mastery in this area.

In this sense, content validity is a "measure" of the adequacy of sampling. We say “measure” in quotation marks, since this type of validity consists of a series of estimates or opinions. These estimates do not provide a quantitative index of validity.

This type of validity is associated above all with achievement tests (mathematics tests, history…). For its determination, the test questions are systematically compared with the behavioral domain of the postulated content.

For example, we have a list of 500 words that we expect students in a course to be able to spell correctly. Then, their performance regarding these words will be important exclusively to test the student's ability to spell all 500 words correctly. However, it will only have content validity to the extent that it provides an adequate sample of the 500 words it represents.