The extent to which relationships between measures/items capture the hypothesized relationships predicted by theory.
Berger, M. et al. 2003. Health Care, Cost, Quality, and Outcomes: ISPOR Book of Terms, Lawrenceville, NJ: International Society for Pharmacoeconomics and Outcomes Research.
Gliner, J.A. and G.A. Morgan. 2000. Research Methods in Applied Settings, Mahwah, NJ: Lawrence Erlbaum Associates.
Rea, P. 1997. Designing and Conducting Survey Research, San Francisco, CA: Jossey-Bass.
Marczyk, G.R. et al. 2005. Essentials of Research Design and Methodology, Hoboken, NJ: John Wiley & Sons.
Shi, L. 1997. Health Service Research Methods, Albany, NY: Delmar Publishers.