1. Suchman EA. Evaluative research: Principles and practice in public service organizations. Washington, DC: Russell Sage Foundation, 1967: 11.
2. Ross PH, Freeman HE, Wright SR. Evaluation: A systematic approach. Beverly Hills, CA: Sage Publications, 1979: 20–32.
3. Fink A, Kosecoff J. An evaluation primer. Beverly Hills, CA: Sage Publications, 1978: 1.