by Are RCTs — really — the best way to establish causality? The best method is always the one that yields the most convincing and relevant answers in the context at hand. We all have our preferred methods that we think are underused. My own personal favorites are cross-tabulations and graphs that stay close to the data; the hard work lies in deciding what to put into them and how to process the data to learn something that we did not know before, or that changes minds. An appropriately constructed picture or cross-tabulation can undermine the credibility of a widely believed causal story, or enhance the credibility of a new one; such evidence is more informative about causes than a paper with the word “causal” in its title. The art is in knowing what to
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Are RCTs — really — the best way to establish causality?
The best method is always the one that yields the most convincing and relevant answers in the context at hand. We all have our preferred methods that we think are underused. My own personal favorites are cross-tabulations and graphs that stay close to the data; the hard work lies in deciding what to put into them and how to process the data to learn something that we did not know before, or that changes minds. An appropriately constructed picture or cross-tabulation can undermine the credibility of a widely believed causal story, or enhance the credibility of a new one; such evidence is more informative about causes than a paper with the word “causal” in its title. The art is in knowing what to show. But I don’t insist that others should work this way too.
The imposition of a hierarchy of evidence is both dangerous and unscientific. Dangerous because it automatically discards evidence that may need to be considered, evidence that might be critical. Evidence from an RCT gets counted even if the population it covers is very different from the population where it is to be used, if it has only a handful of observations, if many subjects dropped out or refused to accept their assignments, or if there is no blinding and knowing you are in the experiment can be expected to change the outcome. Discounting trials for these flaws makes sense, but doesn’t help if it excludes more informative non-randomized evidence. By the hierarchy, evidence without randomization is no evidence at all, or at least is not “rigorous” evidence.
The almost religious belief with which its propagators — including ‘Nobel prize’ winners like Duflo, Banerjee and Kremer — portray it, cannot hide the fact that RCTs cannot be taken for granted to give generalizable results. That something works somewhere is no warranty for us to believe it works for us here or that it generally works. Whether an RCT is externally valid or not, is never a question of study design. What ‘works’ is always a question of context.
Leaning on an interventionist approach often means that instead of posing interesting questions on a social level, the focus is on individuals. Instead of asking about structural socio-economic factors behind, e.g., gender or racial discrimination, the focus is on the choices individuals make. Duflo et consortes want to give up on ‘big ideas’ like political economy and institutional reform and instead solve more manageable problems ‘the way plumbers do.’
Yours truly is far from sure that is the right way to move economics forward and make it a relevant and realist science. The ‘identification problem’ is certainly more manageable in plumbing, but we should never forget that clinical trials and medical studies have another dimensionality and heterogeneity than what we encounter in most social and economic contexts.
A plumber can fix minor leaks in your system, but if the whole system is rotten, something more than good old-fashioned plumbing is needed. The big social and economic problems we face today will not be solved by plumbers performing interventions or manipulations in the form of RCTs.
The present RCT idolatry is dangerous. Believing randomization is the only way to achieve scientific validity blinds people to searching for and using other methods that in many contexts are better. Insisting on using only one tool often means using the wrong tool.
Randomization is not a panacea. It is not the best method for all questions and circumstances. Proponents of randomization make claims about its ability to deliver causal knowledge that is simply wrong. There are good reasons to share Deeaton’s scepticism on the now popular — and ill-informed — view that randomization is the only valid and the best method on the market. It is not.