•Test taker's temporary psychological or physical state. Test performance can be influenced by a person's psychological or physical state at the time of testing. For example, differing levels of anxiety, fatigue, or motivation may affect the applicant's test results.
•Environmental factors. Differences in the testing environment, such as room temperature, lighting, noise, or even the test administrator, can influence an individual's test performance.
•Test form. Many tests have more than one version or form. Items differ on each form, but each form is supposed to measure the same thing. Different forms of a test are known as parallel forms or alternate forms. These forms are designed to have similar measurement characteristics, but they contain different items. Because the forms are not exactly the same, a test taker might do better on one form than on another.
•Multiple raters. In certain tests, scoring is determined by a rater's judgments of the test taker's performance or responses. Differences in training, experience, and frame of reference among raters can produce different test scores for the test taker.
Principle of Assessment: Use only reliable assessment instruments and procedures. In other words, use only assessment tools that provide dependable and consistent information.
These factors are sources of chance or random measurement error in the assessment process. If there were no random errors of measurement, the individual would get the same test score, the individual's "true" score, each time. The degree to which test scores are unaffected by measurement errors is an indication of the reliability of the test.
Reliable assessment tools produce dependable, repeatable, and consistent information about people. In order to meaningfully interpret test scores and make useful employment or career-related decisions, you need reliable tools. This brings us to the next principle of assessment.