This is part of Responsive Translation’s blog post series on the foundations of assessment.

Test reliability is a psychometric term that refers to how stable and consistent an assessment’s results are over time and among test takers. What’s more, test reliability is one of the primary principles driving the gold standard of high-stakes assessment and its translation and adaptation today, along with equivalence, validity and fairness.

Test Reliability in Action

Imagine getting into a car and pressing down on the accelerator with your foot. You would generally expect the car to move forward. And if your neighbor does the same thing, he would expect the same result. Perhaps your neighbor would end up moving faster or slower than you, but still you would both generally expect the car to move forward. Yet, if you pressed down on the car’s accelerator again and this time you teletransported to a different planet, you would not have reliably received the expected result. In fact, you would probably wonder what the heck happened to the car!

Subtypes of Test Reliability

Once you’re comfortably back on this planet, we can express and assess test reliability in different ways, including these three common subtypes:

• Test-retest reliability: Like we saw in the earlier example, when conditions remain the same, it’s reasonable to expect results within a certain range. Test-retest reliability ensures that successive measurements produce consistent and repeatable results.
• Inter-rater reliability: Not all tests are multiple choice or have only one right answer. When tests rely on more subjective types of assessment—such as essay writing—grader agreement becomes more difficult, as humans don’t always interpret or evaluate answers in exactly the same way. Using a variety of methods, inter-rater reliability establishes that assessment decisions continue to meet the same consistent standard across the board.
• Parallel-forms reliability: Sometimes more than one version of a test is needed—with equivalence for all intents and purposes. Parallel-forms reliability means that multiple tests are shown to be consistently equivalent assessments that measure the same construct, knowledge or skill and result in the same observed variances.

Of course more subtypes of test reliability exist, but the principle remains the same: test reliability ensures the stability and consistency of high-stakes assessments for greater test integrity. And isn’t that something we all want?

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Image credit: Expect Best