Aims: To explore and explain the different concepts of reliability and validity as they are related to measurement instruments in social science and health care.
Background: There are different concepts contained in the terms reliability and validity and these are often explained poorly and there is often confusion between them.
Design: To develop some clarity about reliability and validity a conceptual framework was built based on the existing literature.
Results: The concepts of reliability, validity and utility are explored and explained.
Conclusions: Reliability contains the concepts of internal consistency and stability and equivalence. Validity contains the concepts of content, face, criterion, concurrent, predictive, construct, convergent (and divergent), factorial and discriminant. In addition, for clinical practice and research, it is essential to establish the utility of a measurement instrument.
Relevance to clinical practice: To use measurement instruments appropriately in clinical practice, the extent to which they are reliable, valid and usable must be established.