Have you ever weighed yourself in the morning, and then again in the afternoon? If you did, you probably got slightly different readings each time. So how much do you weigh? Which is the correct reading (if either of them is indeed ‘correct’)? Most people answer this question with the obvious response (‘the lower one’), but at the heart of the issue is the reliability of the measurement: its accuracy and consistency over time, and context.
Reliability in the assessment of student learning is also about accuracy and consistency and, as a rule, the higher the stakes of the decision we want to make based on assessment information, the more accurate and consistent we want the information to be. High-stakes decisions need highly reliable information. As we saw with validity, a determination of how reliable an assessment needs to be is informed by its intended end uses.
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