Reliability in Psychology: Definition & Concept

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  • 0:01 Definition of Reliability
  • 0:38 Determining Reliability
  • 1:40 Example of Reliability
  • 3:28 Lesson Summary
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Lesson Transcript
Instructor: Chris Clause
In this lesson, you will learn how the concept of reliability is applied to psychological assessment measures. Following this lesson, you will have the opportunity to test your knowledge with a short quiz.

Definition of Reliability

Reliability is the ability of a test or assessment to yield the same results when administered repeatedly. It would be hard to trust the results of a test that yields strikingly different results when administered to the same participant in close proximity in time to one another. A test that is reliable is not necessarily valid or measuring what it is intended to measure. A test can be reliably inaccurate. Reliability is one important aspect of assessment quality and something that assessment designers and administrators pay close attention to.

Determining Reliability

In the world of psychology, reliability is most often associated with things like intelligence tests, behavioral assessments, and self-report measures. Any time researchers are interested in gathering information or asking questions, they want to be certain that the tools they use to collect information are reliable.

Reliability is determined by calculating the correlation coefficient between repeated sets of assessment scores. If the correlation coefficient is .80 or higher, then it's typically considered to be a reliable test. Notice that in order to be considered reliable, a test does not have to yield a perfect positive correlation of 1.0. Even the most accurately designed tests are not perfect. Factors such as poorly designed questions and format can impact scores and subsequently influence the reliability coefficient. Another factor is the fact that, the more test subjects are exposed to questions, the more familiar with the questions they become.

Example of Reliability

Let's take a look at an example to help illustrate the concept of reliability.

Charlie is a research psychologist who has been studying memory. He believes that he has developed a highly accurate short-term memory assessment. An important part of evaluating how useful his new assessment might be is determining how reliable this new measure of short-term memory is. His assessment yields possible scores from 0-100, with 0 representing weak and 100 representing strong short-term memory abilities. Charlie recruits 15 subjects to take his new short-term memory test, records their scores, and then asks them all to take the same short-term memory test the next day. Their results can be seen in the table below:

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