Internal Consistency Reliability: Example & Definition

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  • 0:01 What Is Reliability?
  • 1:59 Internal Consistency…
  • 3:03 Methods of Measurement
  • 3:47 Examples
  • 4:20 Lesson Summary
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Lesson Transcript
Instructor: Yolanda Williams

Yolanda has taught college Psychology and Ethics, and has a doctorate of philosophy in counselor education and supervision.

Internal consistency reliability is a measure of how well the items on a test measure the same construct or idea. Learn more about internal consistency reliability from examples and test your knowledge with a quiz.

What Is Reliability?

Suppose that you are a psychologist. A client walks into your office and tells you that she has been having nightmares and scary thoughts. She explains that her symptoms started a few days after she survived a car accident. She also reports having flashbacks of her car accident every time she tries to drive a car. She has been taking the bus and relying on friends to take her everywhere she needs to go.

After talking with her for a bit longer, you notice that the symptoms that she is describing sound a lot like post-traumatic stress disorder (PTSD). You decide to search for a psychological test that is designed help you to detect and diagnose PTSD.

You come across the Posttraumatic Stress Diagnostic Scale (PDS). The test manual indicates that the PDS is a valid measure of PTSD. This means that the PDS is accurately able to measure PTSD. You begin to wonder about the consistency, or reliability, of the PDS results. That is, will the PDS produce the same results over and over again?

There are four types of reliability that you can explore:

  • Inter-rater reliability: In instances where there are multiple scorers or 'raters' of a test, the degree to which the raters' observations and scores are consistent with each other
  • Parallel forms reliability: In instances where two different types of a measurement exist, the degree to which the test results on the two measures is consistent
  • Test-retest reliability: The degree to which the measurement's results are consistent over time
  • Internal consistency: The degree to which every test item measures the same construct

Internal Consistency Reliability Defined

Internal consistency is a method of reliability in which we judge how well the items on a test that are proposed to measure the same construct produce similar results. For example, a question about the internal consistency of the PDS might read, 'How well do all of the items on the PDS, which are proposed to measure PTSD, produce consistent results?' If all items on a test measure the same construct or idea, then the test has internal consistency reliability.

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