Summary • Causation, in the statistical sense, means that when we intervene, the chances of different outcomes are systematically changed. • Causation is difficult to establish statistically, but well-designed randomized trials are the best available framework. • Principles of blinding, intention-to-treat and so on have enabled large-scale clinical trials to identify moderate but important effects. • Observational data may have background factors influencing the apparent observed relationships between an exposure and an outcome, which may be either observed confounders or lurking factors. •
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