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Psychometric Properties   | 3 Min Read

How Reliable are Your Psychometric Tests?

Written By Tonmoy Shingal

Psychometric Test Reliability refers to how consistent a measure is a certain element over a period and between two different subjects tested. In other words, does the test measure what it is supposed to measure? It is the consistency in the measurement tool to produce scores by which interpolations can be made.

For instance, a test measuring intelligence should yield the same score for the same person after he or she has completed the rest each time within a short period of time in between (provided the test taker has not changed regarding his/her intelligence over a period of time).

Types of Psychometric Test Reliability

  • Parallel Forms Reliability:

When two tests that are different use the same content but separate procedures or equipment, and yield results that are the same for each test taker.

  • Internal Consistency Reliability:

Items within the test are examined to see if they appear to measure what the test measures. Internal reliability between test items is referred to as internal consistency.

  • Inter-Rater Reliability:

When two raters score the psychometric test in the same way, inter-scorer consistency is high.

  • Test-Retest Reliability:

This is when the same test is conducted over a period of time, and the test taker displays consistency in scores over multiple administrations of the same test.

Factors Influencing Psychometric Test Reliability: What to Watch Out For? 

There are always minor discrepancies in psychometric test reliability. Moreover, individuals taking the same psychometric test may have different thoughts, feelings or ideas at different points in the time leading to variance in scores. A lot of factors (both stable traits and momentary issues) can result in variation in test scores.

Stable traits include weight, height, and other such characteristics. Momentary inconsistency is attributed to different things such as the health of the test-taker, his understanding of a particular test item and so forth.


Why Psychometric Test Reliability Counts

Reliability is essential for psychometric tests. After all, what is the point of having the same test yield different results each time, especially if scores can affect employee selection, retention, and promotion?

Errors in Reliability

Psychometricians identify two different categories of errors:

  • Systematic errors: These are factors pertaining to test construction and are inbuilt in the test.

  • Unsystematic errors: These are errors resulting from random factors such as how the test is given or taken.

Numerous factors influence test reliability. The timing between two test sessions affects test-retest and alternate/parallel forms reliability. The similarity of content and expectations of subjects regarding different elements of testing affects only the latter type of reliability along with split half and internal consistency.

Changes in subjects over time such as their environment, physical state, emotional and mental well-being also need to be considered while assessing the reliability of psychometric tests. Test-based factors such as inadequate testing instructions, biased scoring lacking in objectivity and guessing on the part of the test-taker also influence the reliability of tests. Tests can generate reliable estimates sometimes and not so stable results other times (Geisinger, 2013).

So, just how reliable is your test? Well, it all depends on these factors:

Construction of Items/ Questions

Test designers construct questions on the psychometric test to assess a mental quality (for example motivation). The test questions difficulty level or the confusion they create through ambiguity can influence reliability in a negative way. Biases in interpreting the items as well as errors in question construction can only be corrected if test instructions are properly implemented, and the redesign and research process is active and ongoing.


Administration of the test is another area where systemic errors can creep in. Instructions accompanying the analysis should be clear cut and well defined. Errors in instructions provided to test taker or administrator can have multiple adverse effects on the reliability of the test. Instructions that affect accurate interpretation lower test reliability.


Reliability also means that the test has a particular scoring system, by which interpretation of results is possible. All tests comprise instructions on scoring. Errors such as conclusions without basis or substantial proof can lower the reliability of the test. Test construction is associated with research to provide evidence for the conclusions drawn. If there is a systemic error in the test design phase, this can impact reliability too.

Environmental Factors

Excessive extremes in temperature or distractions of an audio-visual nature can influence test scores regarding reliability. Errors made in administering the psychometric test can also impact the reliability of scores obtained. Human error is possible too, and interpretation or scoring can be influenced by the examiner’s attitude towards the test taker.


The person being examined may suffer from social desirability concerns and give answers that are not reflective of actual choices. Other factors that influence test takers include anxiety, bias, physical factors like illness or lack of sleep. Reliable tests cannot give the real score of the examinee. They can only provide a blend of the actual score and the error score.

psychometric-testHow to Overcome Psychometric Test Reliability Issues

  • Test Length: 

Increasing test length can be a way to improve reliability. The longer the test, the more reliable it is considered.

  • Speed Test:

Speed versus power in psychometric testing is an age-old debate. Speed tests are designed to ensure all students cannot complete the items. Power tests provide items of normal difficulty and ensure that students have ample opportunity to complete the psychometric test. Test takers can be evaluated with reliability if a test has items which can be completed. Speed tests cannot be measured using internal consistency, parallel form or test-retest method.

  • Group homogeneity:

This is another factor whereby the more heterogeneous the scores of the test, the more reliable its measures will be.

  • Item Difficulty:

When there is low variability among test scores, reliability decreases. If the test is so easy that every test taker can easily complete it, how will it serve as a measure of individual differences?


Psychometric Test Reliability Score = Well Framed Items

Difficult, loaded or anxiety-inducing items can hamper the reliability of the test. Care needs to be taken while framing the questions.

Ultimately psychometric test reliability translates into the minimum variance of the scores over time for the same scorer. Keeping these factors in mind can help researchers to design better tests, and psychometricians to implement them correctly.

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Topics: Psychometric Properties

Originally published December 05 2019,updated May 27 2020

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