1. Cronbach, L., S. Ambron, S. Dornbusch, R. Hess, R. Hornik, D. Phillips, D. Walker, and S. Weiner, Toward Reform of Program Evaluation, San Francisco: Jossey Bass, 1980.
2. Sudman, S., and N, Bradburn, Asking Questions, San Francisco: Jossey Bass, 1982.