Factors Affecting Test Score Reliability in Education

Group Variability and Its Impact on Test Scores

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When it comes to testing there are many things that can affect the validity of the test being administered. Kubiszyn and Borich (2016) state, a test is reliable only if a student can take it more than once and receive near the same score. Things such as group variability, scoring reliability, test length, and item difficulty can all affect test score reliability.

Group variability, which is sometimes called the error group, is a term used that refers to variations caused by differences within individual groups. Not all the students within each group are the same. Students have different learning levels and abilities, and this can affect the measurement. 

Scoring reliability refers to the consistency with which different people who score the same test agree on the measurement. This one can be tricky because not every teacher will grade the material the same way, especially if the assessment is answering discussion questions or writing a paragraph. There will be a great deal of variation in this type of assessment.

Reliability has a definite relation with the length of the test. The more the number of items the test contains, the greater will be its reliability and vice-versa. The more sample of items we take of a given area of knowledge, the more reliable the test will be. If I were to take a five-question multiple-choice test and got three of them wrong, it would look like I did not know the material. However, if I missed three questions on a 30-question test, it would look like I did well and understood the material.

Item difficulty on a test can affect the validity as well. I have seen many tests this year in third grade where the information has been too difficult for the students, and only a handful of them performed well without proper preparation. On the other hand, if the test is too easy it can affect validity as well.

For everything that was written in the past was written to teach us, so that through the endurance taught in the Scriptures and the encouragement they provide we might have hope (New International Version, 1984, Romans 15:4). When creating or selecting a test for students to take the teacher must make sure it is assessing what it is meant to assess. Not too easy, not too difficult and the length is appropriate for the students it is being presented to.  At the end of the day, we as teachers must do the best that we can to provide assessments well suited for our students that will help them become successful in the future.

Scoring Reliability and Its Importance for Test Results

Testing is very interesting when it comes to education. When I think of test in the classroom or in education variability and reliability needs to be the very focus of all test. I believe that length  and difficulty is focus more than the variability and reliability. All elements are important to include difficulty and length, however variability and reliability at the forefront.

Group variability results from classes being made up of students with different learning styles, from different culture backgrounds, different perceptions of subject matters, and other factors that create differences in learners. This affect test scores that would differ because the students differ. Mitigating group variability can be accomplished by conducting a pre and post test to determine the amount of variability across the group.

This would also assist in detecting where variability exist so that lesson plans can be adapted. The focus here is to determine which students have grades that are outliers as well as those that fall outside of acceptable deviations from mean. Kubiszyn and Borich (2016, p. 310) discuss this concept, for “group variability affects the size of the reliability coefficient; higher coefficients results from heterogeneous groups from homogenous groups.”

Scoring reliability is the ability of test to provide consist assessment scores. This is determined by students scoring the same when taking the test multiple times, and different teachers arriving at the same grade, when scoring the same test. It also means the same scoring rubric can be applied to different sets of students. This issue can be mitigated by training all teachers on the rubric use to grade assignments, giving teachers smaller class sizes, using objective versus subjective test, limiting the complexity of test questions and reducing the difficulty of evaluation methods. There should also be clarity in test that clearly align with the lesson and using test that are not redundant that tie to other graded items.

The length of test affect test score reliability when test are too long and too short. Test that are too short may not adequately. Test that are too long may inflate the reliability of scores. Test should be long enough to cover material and mitigate the chance that students are guessing. Their length should be tied to an appropriate time limit where enough questions are asked to assess student knowledge. Kubiszyn and Borich (2016, p. 313) “test length affects score reliability; as test length increases, the test score reliability tends to go up.” Care should be taken to not ask redundant questions or make the questions too difficult.

Item difficulty also affects reliability. The goal of test is to measure student performance based on material taught. Therefore, the test should be simple in terms of testing what was taught. This issue can be mitigated by using moderate item difficulty that focuses on the course material, while challenging student knowledge.