Which error is classified as a constant error in test scores?

The halo effect is classified as a constant error in test scores because it occurs when an evaluator's overall impression of a test-taker positively or negatively influences the ratings or scores assigned to specific traits or abilities, regardless of the actual performance on those specific items. This bias leads to a consistent distortion in scoring, impacting test outcomes in a uniform way across multiple assessments.

In contrast, measurement errors typically fluctuate based on various factors, such as the conditions under which the test is administered. Sample selection errors depend on the chosen population for testing, which can introduce variability based on who is included or excluded from the sample. Test-taker familiarity relates to how well candidates know the testing process or content, which can alter scores but does not consistently affect every examinee in the same manner. Thus, the halo effect stands out as an error that systematically skews results in a particular direction, embodying the concept of a constant error.