Test reliability is an essential factor that should be considered in the process of designing tests. Kubiszyn and Borich (2016) define the matter as “the consistency with which [a test] yields the same rank for individuals who take the test more than once” (p. 338). In other words, the reliability of a test is its ability to yield similar results in the case of repeated administration. Four variables influence the reliability of tests, including group variability, scoring reliability, test length, and item difficulty. When designing a test, an educator should be aware of their impact and mitigate the possible adverse outcomes.
The first principle of test reliability is with the increase in group diversity is positively correlated with test reliability. In other words, tests conducted in homogeneous groups are less likely to produce reliable results that those conducted in heterogeneous groups (Kubiszyn & Borich, 2016). Since it is usually impossible to increase variance within groups, the only way to mitigate poor reliability is to improve performance in terms of other variables that increase test reliability. At the same time, educators may consider conducting several tests to evade bias.
The second principle is that higher scoring reliability will positively influence the test reliability coefficient. According to Kubiszyn and Borich (2016), if scoring reliability is 0.70, then the maximum test reliability will be 0.70. However, the maximum score is usually not achievable due to other factors. Therefore, educators should employ efficient strategies while scoring tests. In particular, there should be clear marking criteria formulated for all types of questions. Special emphasis should be put on marking essay questions, as there may be a significant inconsistency if two or more educators are involved in the process. The reliability of essay question results can be improved by letting two or more teachers grade them. In short, scoring reliability is vital for test reliability, and teachers can easily control it.
The number of items in a test is also positively correlated with test reliability. Therefore, the third principle, all other factors being equal, the more items included in a test, the higher the reliability of the test results. A relatively small number of questions included in the test may benefit students who did not prepare for the test and penalize better prepared students (Kubiszyn & Borich, 2016). If a test has only two questions, it increases the possibility of passing or failing by chance. Therefore, the matter should be addressed by adding an optimal number of questions to ensure high reliability and an adequate timeframe. However, merely adding the questions does not always mean improving the reliability score. The extra items should be written in a clear manner and address the knowledge and traits that have not been addressed in the test.
The final principle states that if the test is overly complicated or easy, the reliability decreases. Kubiszyn and Borich (2016) state that if the questions are too challenging or straightforward, the score distribution becomes more homogeneous. According to the first principle, the reliability deteriorates when the distribution of scores is less diverse. Therefore, teachers should include a limited number of challenging and simple questions and dedicate more attention to medium-difficulty questions.
In summary, teachers should acknowledge the four principles of test reliability when designing or selecting a test. While group variation may be difficult to address, scoring reliability, number of items, and difficulty of questions can be easily modified. Therefore, educators should dedicate enough resources to evaluation and alteration of tests to avoid bias.
Reference
Kubiszyn, T., & Borich, G., D. (2016). Educational testing & measurement: Classroom applications and practice (11th ed.). Hoboken, NJ: Wiley.