The Classical Test Theory: what it is and what it explains

Tests are scientific instruments widely used in the field of psychology in order to measure an evaluation of aptitudes, knowledge or functions. When a test measures what it claims it is valid, while if it measures well, we could say that it is reliable; being both characteristics very important for a psychological test.

The classic theory of tests (CTT) is that theory of psychological tests that gave rise to a very important branch of psychology, psychometry. This theory pays special attention to achieving the highest accuracy of the measurement possible or, instead, if this is not possible, to obtain the precise determination about the measurement error, that being the reason why it is also known as "measurement error theory". measurement".

In this article we will explain in greater detail what the classical theory of tests consists of. in order to understand its importance within the field of psychology, but first it is convenient that we see what is the origin of this theory.

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What is the origin of the Classical Test Theory?

The classical test theory (TCT) It has its origins at the beginning of the 20th century, by the English psychologist and statistician Charles Edward Spearman. and his research, which in some way meant the beginning of a new area within the field of psychology, psychometry.

Psychometrics is that area of ​​psychology in which specialists are responsible for investigating from theories, methods and techniques involved in measuring and also quantifying various psychological variables of the set of psychic characters of the being human. Within psychometrics, tests are a very important tool, as well as in psychology in general, being some tests that are carried out in order to carry out an evaluation as exhaustive as possible of aptitudes, knowledge or functions.

In addition, within the psychological tests we can find those commonly known tests, of a psychotechnical or psychological nature, which are used with the fundamental objective of evaluating or study a function, so that this type of test has been designed to be able to measure or evaluate various psychological characteristics of people for different purposes (p. g., in the selection tests for a certain job).

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What is the Classical Test Theory?

Classical test theory (CTT) focuses especially on the achievement of the greatest possible measurement accuracy or, instead if this is not possible, to obtain the precise determination about the measurement error, which is why it is also known as "measurement error theory".

In addition, TCT is a theory that is used in the field of psychometrics in order to make an explanation as exhaustive as possible in each case about the way in which starting from From a measured test value of a person, the true value of the personality trait or of the characteristic manifestation of a person or aptitude that is intended could be concluded. to size.

On the other hand, within the test theories, there is also an emphasis on how to evaluate the quality of the test, as well as on how to refine it in order to reduce errors to a minimum. For this reason, it is important to keep two concepts in mind when studying the classical theory of tests, which are reliability and validity.

Reliability, according to test theories, is the stability or consistency of the measurements. in case the measurement process is repeated. In other words, it would be the accuracy or reliability, assuming there were no measurement errors, with which a test is capable of determining the true value. However, the reliability can only be estimated since the true values ​​are not known.

Instead, validity is the degree to which theory and empirical evidence support the interpretation of test scores. In other words, we would say that validity is the ability of an instrument to correctly or adequately and meaningfully quantify the measured trait for which it had been designed.

It should be noted that in the field of psychometrics we could find two main theories that have been developed with the fundamental objective of constructing and analyzing the tests. One of them, the one that supposed the beginning of all this, is what we know as the classic theory of tests (TCT); on the other hand, we can find the second, the item response theory (IRT).

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Explanation of the general process of preparing a test

Now that we have briefly seen what the classical theory of tests (CTT) consists of and what its origins are, it is time to proceed to explain what the general process consists of on how to build a test following the rules of TCT, being noted that these steps are useful for building performance or aptitude tests, as well as also to develop inventories, questionnaires or even scales to measure attitudes, interests, feelings etc

1. Identifying a target

The first step when developing a test following the classical theory of tests would be the search for careful consideration of the purposes for which the scores will be used: prediction, ranking, diagnosis etc. Thus It is important in this step to anticipate the decision processes in which the information that is going to be provided by the test It will be used.

The most common general categories for which questionnaires or tests are normally used would be 4: behavioral or academic assessment, measurement of a theoretical construct, diagnostic classification, or the classification of the staff.

On the other hand, it is very important to keep in mind some elements of the context due to their great relevance, the following being very relevant: temporary restrictions or the time available to apply the test, the characteristics of the population to which the test is directed or if the administration of the test is going to be individual or collective.

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2. The definition of the construct

A psychological construct, also called a hypothetical construct or psychological construct, in psychometrics is a term commonly used to refer to the hypothetical conceptual description about some psychological trait or attribute that is intended to be studied; being therefore a very useful resource to facilitate the understanding of the behavior of the human being. We could say that a construct is a label that is used in the field of psychology to refer to a set of behaviors (p. g., personality, creativity, intelligence, memory, etc.).

Therefore, the second step when developing a test from the classical test theory would be the definition of the construct to be measured. Once the construct has been defined, it would be time to start designing the test.

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3. The test design

In this step you must a planning on the evaluation instrument before moving on to the writing of the test items. This is important because it must be guaranteed that the items will reflect the objective and the definition of the construct that had been developed in the previous step.

4. The wording of your items

When writing the topics, it should be sought that they reflect as accurately as possible the indicator behavior of the previously defined construct. In turn, it is important to avoid, or at least minimize, potential errors that could contaminate inferences. that would be carried out from the scores obtained in the test towards that psychological construct that is to be evaluated.

5. The analysis of the items

The moment the test items have been written is when their quality should be analyzed. In the quality analysis of the items those that will be included in the final version of the test will be selected. For this, it is necessary to look at those that are suitable as a measure of the variable and also their contribution to internally forming a test in a consistent manner.

There are two statistical properties that are normally analyzed when assessing item quality: item discrimination and item difficulty.

6. Analysis of reliability and validity

When the items have been correctly analyzed and there is a final selection with those that can form a test useful to measure what was initially intended, we must proceed to analyze the reliability and validity of the test, Y for this, the test must be administered to a sample of people.

7. Develop rules for interpreting scores

The last step to take into account when developing a test following the norms of classical test theory would be the elaboration of the interpretation norms of the scores. For this, we can find ourselves with two perspectives to follow at the moment in which we want to interpret the execution of a person of a questionnaire or a test: criterion-referenced interpretation or norm-referenced interpretation.

If we choose the interpretation referring to norms, we must take into account that this would imply previously providing information about the performance or execution of the test by making a comparison with the distribution of scores of a reference group or of a sample normative.

In contrast, if we chose a criterion-referenced interpretation, a person's performance would be analyzed in relation to with the criteria or standards that had been previously established regarding the execution of that test or questionnaire.