1. Barber, T. X. (1976). Pitfalls in human research. Elmsford, NY: Pergamon Press.
2. Barrera, R. D., & Sulzer-Azaroff, B. (1983). An alternating treatment comparison of oral and total communication training programs with echolalic autistic children. Journal of Applied Behavior Analysis, 16, 379–394.
3. Campbell, D. T., & Stanley, J. C. (1963). Experimental and quasi-experimental designs for research. Chicago: Rand-McNally.
4. Cronbach, L. J., & Meehl, P. E. (1955). Construct validity in psychological tests. Psychological Bulletin, 52, 281–302.
5. Cook, T. D., & Campbell, D. T. (Eds.) (1979). Quasi-experimentation: Design and analysis issues for field settings. Chicago: Rand-McNally.