We know that psychology uses the application of tests to make inferences about people. But, what do the scores obtained in these tests refer to? This is the responsibility of validity. In addition, as we have already explained in another article, there is not only one type of validity, but several. In this space we explain what predictive validity is responsible for.
The researcher Robert Thorndike (1989) explains that the validity of a test is related to what this test tries to measure. Thus derived from this premise, the question arises: is it appropriate to use or interpretation of scores of this test ?, Or: What generalizations can be made without entering a very large range of error from the results the proof? Validity refers to all these questions.
Definition of validity
In statistical terms, validity is defined as the proportion of the true variance that is relevant for the purposes of the test. What does the relevant term mean? In this case, we refer to the characteristics or dimensions that the test we are using is capable of measuring.
As we mentioned previously, the validity of a test is defined:
- Through the relationship between their scores with some measure of external criteria.
- That is, if we have another test that measures the same, we would compare the results obtained with both, understanding that the new test measures the same as the first when the results are similar.
- By means of the extent to which the test measures a hypothetical specific underlying trait or “construct”. In this case, a common practice is to compare the results of two parts of the test intended to measure the same. It is considered that the validity with greater correlation / association between the results, the validity is greater.
Types of validity
As we mentioned previously, there are several types of validity. Specifically, the types of validity are:
- Content validity (or evidence of content).
- Predictive validity (or external evidence).
- Construct validity
- Predictive validity (or external evidence)
Do the test scores predict a performance or future behavior? External validity deals with answering this question.
Commonly in psychology tests are used to predict possible future behaviors. Thus, we use the test to help us make some practical decision (classification, selection, etc.). In each of these situations, the greater the accuracy of the prediction, the greater is the predictive validity of the test and, therefore, the test will be more useful. (one)
For example, let’s say we use a test in a case of personnel selection. In such a case, the test will be an acceptable component of the personnel selection process as long as their scores predict the execution of some important component of the work to which the interviewees aspire. This would be called an external criterion.
Thus, the researcher Jaime Aliaga says that for the test to be used as part of a process of selection of necessary personnel, as you can imagine, that the test has a good validity. In this sense, the idea is to relate the test with the relevant criteria. Then, it seems that the fundamental interest of the psychologist or evaluator is to determine if the test that is measured predicts a certain criterion.
To achieve this, says researcher Aliaga, we need that the external criteria with which the test scores will be related are reliable and valid criteria. But what are we talking about when we talk about the criterion?
The criterion in predictive validity
According to Aliaga, a criterion is any performance that subjects have in real life. For example, a criterion could be the measure of work performance or the measure of academic performance in the case of a student. We could talk about many more types of these criteria. The problem, says Aliaga, is that in many cases it is impossible to find an unambiguous criterion of a mental trait.
Let’s say, for example, that two psychologists investigate together the academic performance of a certain number of students. Thus, investigating the same thing, the two psychologists can use different criteria. For example, the first psychologist could consider as criterion the scores obtained in the exams. The second could consider that the correct criterion is the time it takes each student to complete each task.
When we want to validate a test, the predictive validity of a test (as well as concurrent validity) is usually expressed by a correlation coefficient between the scores we call criterion. This coefficient is called the validation coefficient. According to Aliaga, the interpretation of this coefficient requires an excellent domain of the statistical analysis used to obtain this criterion. After obtaining the criterion, the following that will be important to obtain the category of validity are the statistical procedures that are used.
What is the predictive validity for?
Thus, predictive validity is one of the types we need to determine the validity of a test. Logically, and specifically in the field of psychology, a test is better the more validity it possesses. In addition, we must bear in mind that the key aspect of this type of validity is the criterion. We need tests that serve as reliable and valid criteria. With this, we can correctly determine the predictive validity.