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What's the Difference Between Reliability and Validity?
What's the Difference Between Reliability and Validity?

Understand the differences between reliability and validity and why these measures are essential components of any effective assessment.

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Written by Wonderlic Consulting
Updated over a week ago

Reliability and validity are critical components of any assessment. In recent years, these terms have become more commonplace, which has led to misunderstandings about their definitions as they pertain to assessments. This article will highlight what each term means and how they are differentiated.


Validity refers to how well an assessment measures what it is supposed to measure. For example, a valid personality assessment would generate scores that reflect meaningful differences in personality. It's important to consider two key factors to understand validity.

  • A test is only valid with respect to something specific. Because no test is valid for measuring everything, saying a test is valid is meaningless without a description of what the test is designed to validly measure. For example, a cognitive ability test may be a valid measure of general intelligence, but it's unlikely to be a valid measure of driving ability.

  • Validity is variable. This means that an assessment's validity changes based upon what it's stated to measure. For example, Wonderlic's family of cognitive ability tests are valid for measuring a candidate's cognitive ability, but they are far less likely to be valid measures of a candidate's fit to a company's culture.


Reliability relates to an assessment's ability to provide the same or similar results across repeated administrations or over time. To visualize reliability, consider a target at an archery range. An assessment of archery skills can be considered reliable if the archer hits roughly the same spot on the target regardless of how many arrows are shot or the amount of time between shots. Furthermore, if the archer is able to group the arrows similarly on a nearly identical target, this further demonstrates reliability.

Two of the most noteworthy types of assessment reliability are:

  • Test-Retest Reliability:  This represents an individual's ability to receive the same or a similar score on an assessment despite repeated administrations. For Wonderlic's family of cognitive ability assessments, this represents a candidate's ability to score similarly on two administrations despite there being minutes, days, or weeks between administrations.

  • Parallel or Alternate Forms Reliability:  Because the goal of creating multiple forms of an assessment is to ensure they are roughly equivalent, parallel and alternate forms reliability indicates the degree to which different forms of an assessment are related to each other. Parallel and alternate forms reliability differ slightly because it may be impossible to confirm if forms are truly parallel. With alternate forms reliability it is assumed that a best effort has been made to ensure the forms are as equivalent as possible. An example of alternate forms reliability would be a candidate receiving the same or very similar scores on Wonderlic cognitive ability tests, regardless of the form of the test that was administered.

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TAGS: Reliability, Validity, Reliable, Valid

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