Textbook
Stephen L. Morgan, & Winship, C. (2007). Counterfactuals and Causal inference. Cambridge University Press.
Other sources
Heckman, J. J., & Smith, J. A. (1995). Assessing the case for social experiments. The Journal of Economic Perspectives, 9(2), 85-110.
Concato, J., Lawler, E. V., Lew, R. A., Gaziano, J. M., Aslan, M., & Huang, G. D. (2010). Observational methods in comparative effectiveness research. The American journal of medicine, 123(12), e16-e23.
Kaptchuk, T. J. (2001). The double-blind, randomized, placebo-controlled trial: gold standard or golden calf?. Journal of Clinical Epidemiology, 54(6), 541-549.
Stuart, E. A. (2010). Matching methods for causal inference: A review and a look forward. Statistical science, 25(1), 1.
Austin, P. C. (2008). A critical appraisal of propensity‐score matching in the medical literature between 1996 and 2003. Statistics in medicine, 27(12), 2037-2049.