Classical test theory: what is it and what does it explain?

Tests are scientific instruments widely used in the field of psychology to measure and assess skills, knowledge or functions. When a test measures what it claims to be valid, when it measures well, it could be said to be reliable; both characteristics being very important for a psychological test.

Classical Test Theory (TCT) is that theory of psychological testing that gave rise to a very important branch of psychology, psychometrics. This theory pays particular attention to obtaining the greatest possible precision of the measurement or, on the contrary, if this was not possible, to the precise determination of the error of measurement, this is the reason why it is also known as the “measurement error theory”.

In this article, we will explain in more detail what is the classical test theory. in order to understand its importance in the field of psychology, but it is necessary first to see what is the origin of this theory.

    What is the origin of Classical Test Theory?

    Classical Test Theory (TCT) it has its origins at the beginning of the 20th century, from the hand of the English psychologist and statistician Charles Edward Spearman and his research, which in a way meant the beginning of a new field in the field of psychology, psychometrics.

    Psychometrics is the field of psychology in which specialists are responsible for investigating on the basis of the theories, methods and techniques involved in the measurement and quantification of various psychological variables of the set of psychic characteristics of the human being. Within psychometrics, tests are a very important tool, as well as in psychology in general, being tests that are carried out in order to carry out the most complete evaluation possible of skills, knowledge or functions.

    Also, in the psychological tests we can find the commonly known tests, of a psychotechnical or psychological nature, which are used with the fundamental objective of evaluating or studying a function, so this type of test has been designed to be able to measure or evaluate various psychological characteristics of people with different purposes (for example, during selection tests for a specific job).

      What is Classical Test Theory?

      Classical Test Theory (TCT) focuses particularly on obtaining the greatest possible accuracy of the measurement or, in its place if this was not possible, to obtain the precise determination of the measurement errorthis is why it is also called “theory of measurement error”.

      In addition, the 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 on how from a measured test value a person could come to conclude the true value of the personality trait or characteristic manifestation of a person or of an aptitude that one wishes to measure.

      On the other hand, within the test theories, there is also an impact on how to assess the quality of the tests, as well as how to debug it to minimize the error. This is why it is important to keep two concepts in mind when studying classical test theory, which are reliability and validity.

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

      In place, validity is the degree to which theory and empirical evidence support the interpretation of test results. 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 was 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 building and analyzing tests. One of them, the one that started all of this, is what we call classical test theory (CTT); on the other hand, we find the second, item response theory (IRT).

        Explanation of the general process for preparing a test

        Now that we have seen briefly what Classical Test Theory (TCT) is and what its origins are, it is time to proceed with the explanation. what is the general process on how to construct a test following the rules of the TCTit should be noted that these steps are useful for constructing performance or aptitude tests, as well as for developing inventories, questionnaires or even scales to measure attitudes, interests, feelings, etc.

        1. Identifying a goal

        The first step in developing a test following classical test theory would be to carefully research the purposes for which the scores will be used: prediction, classification, diagnosis, etc. That is why it is important in this step to anticipate the decision-making processes in which the information that will be provided by the test 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 personnel classification.

        On the other hand, it is very important to have certain elements of the context present because of their great relevance, the following being very relevant: the temporal constraints or the time available to apply the test, the characteristics of the population to which it is aimed at the test or if the administration of the test will be individual or collective.

          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 of a psychological trait or attribute that is intended to be studied; therefore being a very useful resource to facilitate the understanding of human behavior. You could say that a construct is a label used in the field of psychology to designate a set of behaviors (eg personality, creativity, intelligence, memory, etc.).

          Therefore, the second step when developing a test based on classical test theory would be defining the construct you wish to measure. Once the concept is defined, it would be time to start designing the test.

            3. Test design

            In this step, you have to do planning on the assessment instrument before moving on to writing test items. This is important because it must be ensured that the items will reflect the purpose and definition of the construct that were developed in the previous step.

            4. Writing articles

            When writing the subjects, it is necessary to seek that they reflect as faithfully as possible the indicator behavior of the construct defined above. In turn, it is important to avoid, or at least minimize, potential errors that could contaminate the inferences that would be made from the scores obtained in the test towards that psychological construct that is being assessed.

            5. Item analysis

            It is when the test items have been written that their quality should be analyzed. In the analysis of the quality of articles those who will be included in the final version of the test will be selected. To do this, you need to pay attention to which ones are suitable as a measure of the variable and also their contribution to forming a test internally consistently.

            Two statistical properties are normally analyzed when assessing item quality: item discrimination and item difficulty.

            6. Reliability and validity analysis

            When the articles have been properly analyzed and a final selection is made with those that can form a useful test to measure what was originally intended, we must proceed to the analysis of the reliability and validity of the test, and 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 rules of classical test theory would be the development of the rules for interpreting the scores. For this we can find two perspectives to follow when we want to interpret the execution of a questionnaire or a test by a person: interpretation refers to criteria or interpretation refers to standards.

            If the interpretation referred to the standards is chosen, it should be kept in mind that it would be a question of providing information beforehand on the performance or the execution of the test by making a comparison with the distribution of the scores of a reference group or a normative sample.

            On the other hand, if one were to choose an interpretation referring to the criterion, the execution of a person would be analyzed in relation to the previously established criteria or standards concerning the execution of this test or questionnaire.

            Bibliographic references

            • Abad, FJ, Garrido, J., Olea, J. & Ponsoda, V. (2006). Introduction to psychometrics: classical test theory and item response theory. Madrid: Autonomous University of Madrid.
            • Balluerka, N. & Vergara, AI (2002). Models of experimental research in psychology. Madrid: Pearson Education.
            • Calero, MD and Padilla, JL (2013). Psychometric techniques: tests. In R. Fernández-Ballesteros (coord.). Psychological Assessment: Concepts, Methods and Case Studies (pp. 299-335). Madrid: Ediciones Pyramid.
            • Delgado, C. (2014). Traveling to Ítaca for Quantitative Mothers: Itinerary Guide for Undergraduate and Postgraduate Research. Salamanca: Amarú Editions.
            • Moreno, C. & Ramírez, IM (2019). Psychological assessment: process, techniques and applications in domains and contexts. Madrid: Editorial Sanz y Torres.
            • Muniz, J. (2010). Testing theories: classical theory and item response theory. Notebooks of the psychologist, 31(1), pp. 57-66.
            • Muniz, J. (1998). Classical test theory. Madrid: Ediciones Pyramid.
            • Navas, MJ (2010). Methods, designs and techniques of psychological research. Madrid: National University of Distance Education.
            • Santisteban, C. (2009). Principles of psychometrics. Madrid: summary edition.
            • Spearman, C. (1904). The proof and measurement of the association between two things. The American Journal of Psychology, 15(1), 72-101.

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