Saturday, May 15, 2010

Cartwright on the value of Randomised Trials

Thanks to Graham Brownlow on irisheconomy blog for pointing to this gem (requires subscription).

Nancy Cartwright, ‘What are randomised controlled trials good for? ’, Philosophical Studies, vol. 147, no.1 (2010), pp.59-70.

Abstract Randomized controlled trials (RCTs) are widely taken as the gold standard for establishing causal conclusions. Ideally conducted they ensure that the treatment ‘causes’ the outcome—in the experiment. But where else? This is the venerable question of external validity. I point out that the question comes in two importantly different forms: Is the specific causal conclusion warranted by the experiment true in a target situation? What will be the result of implementing the treatment there? This paper explains how the probabilistic theory of causality implies that RCTs can establish causal conclusions and thereby provides an account of what exactly that causal conclusion is. Clarifying the exact form of the conclusion shows just what is necessary for it to hold in a new setting and also how much more is needed to see what the actual outcome would be there were the treatment implemented.
Keywords Randomized controlled trials (RCTs) External validity
Probabilistic theory of causality Causal inference Capacities Contributions

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