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Reliability

The issue of reliability (i.e., repeatability or reproducibility) is crucial in selecting and developing the most appropriate item, scale, or instrument. Reliability refers to the extent to which an instrument or the measurements of a test will consistently produce the same result, measure, or score if applied two or more times under identical conditions. A technique is reliable, or has achieved a high level of agreement, if it yields consistent results on repetition. If repeated measurements produce different results, and the entity being measured is assumed to not have changed, the instrument would be considered unreliable.

Methods of Assessing or Estimating Reliability

There are a variety of methods for estimating instrument reliability. DeVellis classifies these methods into two categories: (1) the type of instrument (observer or external ...

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