What supports the purpose of a test to measure differences in test performance?

The purpose for which the test is given is fundamental to measuring differences in test performance because it establishes the criteria and context for evaluating the results. A well-defined purpose helps identify what specific competencies, skills, or knowledge the test is intended to assess. When the purpose is clear, the test can be designed to accurately and effectively differentiate performance levels among test takers, ensuring that the results are meaningful and relevant.

In contrast, while the test format, number of items, and reliability of the test can all impact how results are presented and interpreted, they do not inherently determine the appropriateness of the test for its intended purpose. A test can be formatted well and still fail to measure what it is supposed to if the purpose is not aligned with the test's content or objectives. Thus, the underlying intent of administering the test is the cornerstone that supports the accurate measurement of differences in performance.