The process of evaluating a measurement instrument in psychology often begins with assessing its reliability, which refers to the consistency and stability of the measurement over time or across different scorers. Establishing that an instrument produces consistent results is fundamental; without reliability, any further analysis or conclusions drawn from the data could be flawed.
Once reliability has been established, the next step is to evaluate validity. Validity assesses whether the instrument accurately measures what it intends to measure. For instance, if a test claims to measure anxiety, it needs to be shown that the results meaningfully reflect the level of anxiety in respondents. Therefore, for a measurement tool to be effective, it must first be reliable and then valid. This sequence is critical in research and assessment practices, making reliability a prerequisite for establishing validity.