Integrating validity theory with use of measurement instruments in clinical settings

Objective. To present validity concepts in a conceptual framework useful for research in clinical settings. Principal Finding's. We present a three-level decision rubric for validating measurement instruments, to guide health services researchers step-by-step in gathering and evaluating validity evidence within their specific situation. We address construct precision, the capacity of an instrument to measure constructs it purports to measure and differentiate from other, unrelated constructs; quantification precision, the reliability of the instrument; and translation precision, the ability to generalize scores from an instrument across subjects from the same or similar populations. We illustrate with specific examples, such as an approach to validating a measurement instrument for veterans when prior evidence of instrument validity for this population does not exist. Conclusions. Validity should be viewed as a property of the interpretations and uses of scores from an instrument, not of the instrument itself: how scores are used and the consequences of this use are integral to validity. Our advice is to liken validation to building a court case, including discovering evidence, weighing the evidence, and recognizing when the evidence is weak and more evidence is needed.