Measurement Property	Type	What Is Assessed?	FDA Review Considerations
Reliability	Test-retest or intra- interviewer reliability (for interviewer-administered PROs only)	Stability of scores over time when no change is expected in the concept of interest	• Intraclass correlation coefficient • Time period of assessment
	Internal consistency	• Extent to which items comprising a scale measure the same concept • Intercorrelation of items that contribute to a score • Internal consistency	• Cronbach’s alpha for summary scores • Item-total correlations
	Inter-interviewer reliability (for interviewer-administered PROs only)	Agreement among responses when the PRO is administered by two or more different interviewers	• Interclass correlation coefficient
Validity	Content validity	Evidence that the instrument measures the concept of interest including evidence from qualitative studies that the items and domains of an instrument are appropriate and comprehensive relative to its intended measurement concept, population, and use. Testing other measurement properties will not replace or rectify problems with content validity.	• Derivation of all items • Qualitative interview schedule • Interview or focus group transcripts • Items derived from the transcripts • Composition of patients used to develop content • Cognitive interview transcripts to evaluate patient understanding
	Construct validity	Evidence that relationships among items, domains, and concepts conform to a priori hypotheses concerning logical relationships that should exist with measures of related concepts or scores produced in similar or diverse patient groups	• Strength of correlation testing a priori hypotheses (discriminant and convergent validity) • Degree to which the PRO instrument can distinguish among groups hypothesized a priori to be different (known groups validity)
Ability to detect change		Evidence that a PRO instrument can identify differences in scores over time in individuals or groups (similar to those in the clinical trials) who have changed with respect to the measurement concept	• Within person change over time • Effect size statistic