M. Feuer, L. Towne, and R. Shavelson. Educational Researcher, 31 (8):
4(2002)“For example, when well-specified causal hypotheses can be formulated and randomization to treatment and control conditions is ethical and feasible, a randomized experiment is the best method for estimating effects” p. 8.
B. Bannan-Ritland. Kelly, AE; Lesh, RA; Baek, JY Handbook of Design Research Methods in Education: Innovations in Science, Technology, Enginnering and Mathematics Learning and Teaching. New York: Routledge, (2008)