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Reliability pertains to the degree of trustworthiness associated with a test score, a concept extensively explored in Chapter 2, “The Language of Assessment,” and Chapter 10, “Establishing Evidence of Reliability and Validity.” In our sample from Table 11.1, the reliability coefficient is denoted as alpha, with a value of 0.754.
What level of reliability should you anticipate from the outcomes of your classroom assessments? This answer varies but is intricately tied to the confidence required for decisions based on test results. High-stakes decisions necessitate highly reliable measurements. In simpler terms, a test whose results dictate whether a student graduates from a program of study demands a high level of reliability. Consequently, basing such significant decisions solely on one classroom exam is strongly discouraged.
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NURS-6052 Module 2: Quiz – IS IT QUANTITATIVE, QUALITATIVE, OR MIXED METHODS?
Miller, Linn, and Gronlund (2009) concur that the necessary degree of reliability for classroom test results depends largely on the nature of the decision driven by these results. Consider the gravity of the decision and whether it can be reversed. When a test’s reliability coefficient is low, it is crucial to make tentative decisions, gather additional data, and, most importantly, be open to reversing a decision.
Miller et al. (2009) report that the reliability coefficients for teacher-made tests typically range between 0.60 and 0.85. Kehoe (1995) argues that test results with more than 50 items should exhibit reliability coefficients greater than 0.80, while Frisbie (1988) asserts that teacher-made test results should yield reliability coefficients averaging around 0.50, with 0.85 being the generally accepted minimum reliability standard when individual decisions are based on a single test score. Frisbie also notes that reliability coefficients of approximately 0.50 for teacher-made test results can be tolerated when these scores are combined with other scores to assign a grade. In such cases, the focus should be on the reliability of the composite score resulting from the combination of scores.
At first glance, our sample’s reliability coefficient of 0.754 appears respectable by these standards. However, it should not be evaluated in isolation. Various factors influencing the reliability coefficient of a test must be taken into consideration. These factors, exhaustively discussed in Chapter 10, “Establishing Evidence of Reliability and Validity,” encompass the following:
1. Quality of the test items
2. Item difficulty
3. Item discrimination
4. Homogeneity of the test content
5. Homogeneity of the test group
6. Test length
7. Number of examinees
8. Speed
9. Test design, administration, and scoring
When scrutinizing the reliability coefficients of your classroom test results, it is imperative to account for these factors. For instance, if you are dealing with a class of highly homogeneous high-achieving students, you might obtain a low reliability coefficient on a test featuring challenging, well-constructed, heterogeneous items that adhere to all the guidelines outlined in this text. Conversely, a low reliability coefficient might signify that the items are either overly difficult or too easy for the student group. On the flip side, a high reliability coefficient may result from a speeded test containing numerous narrowly defined content items administered to a large, heterogeneous student group. It is essential to bear in mind that testing conditions, teaching quality, and the number of questions and examinees all factor into the reliability of test scores. In most cases, low reliability coefficients stem from an abundance of either very easy or exceedingly difficult items, inadequately crafted items lacking discriminative power, or test items failing to represent a coherent body of content (Kehoe, 1995).
Interpreting a reliability coefficient for test results necessitates considering all these influential variables. A test boasting a low reliability coefficient may still yield dependable outcomes. Your judgment constitutes a critical component of this equation. As Mark Twain famously quipped, “There are three kinds of lies: lies, damned lies, and statistics.” In isolation, statistical findings lack meaning and can be manipulated to support misguided interpretations. Your informed interpretation of the data infuses fairness into your grading decisions. For an in-depth exploration of reliability estimates for classroom exams, refer to Chapter 10, “Establishing Evidence of Reliability and Validity.”
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