Answers are grounded in this paper and cite their sources.
Before R. A. Fisher introduced randomized experimentation, the literature on empirical methods emphasized reducing heterogeneity of experimental units as the key to inference about the effects caused by treatments. To what extent is heterogeneity relevant to causal inference when ethicalor practical constraints make random assignment infeasible?
No takes yet. Share an insight, caveat, or question.
Paul R. Rosenbaum (2005) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: