Thursday, March 30, 2017

Statistics and Gelman

Russ Roberts had a fantastic conversation with Andrew Gelman on a recent podcast. It covered a lot of issues and examples, some of which were familiar.

A particularly salient metaphor "the Garden of Forking Paths" crystallized (for me) some unintentional p-hacking by people with integrity.
In this garden of forking paths, whatever route you take seems predetermined, but that’s because the choices are done implicitly. The researchers are not trying multiple tests to see which has the best p-value; rather, they are using their scientific common sense to formulate their hypotheses in reasonable way, given the data they have. The mistake is in thinking that, if the particular path that was chosen yields statistical significance, that this is strong evidence in favor of the hypothesis.
This is why replication studies in which "researcher degrees of freedom" are taken away have more reliable scientific content. Unfortunately, they are unglamorous. Often, in the minds of the general population, they do not replace the flawed original study.

Gelman discusses numerous such examples on his blog. These include studies on "priming" and "power poses" that have failed to replicate. Sure there is the element of schadenfreude, but what I find far more interesting is the response of scientists who championed a theory react to new disconfirming data. For instance, Daniel Kanheman recently admitted that he misjudged the strength of the scientific evidence on priming, and urged readers to disregard one of the chapters devoted to it in his best-seller "Thinking Fast and Slow". Similarly, one of the coauthors of the original power poses work, Dana Carney, had the courage to publicly change her mind.

That is what good scientists do. They update their priors, when new data instructs them to do so.

This brings me to another health and nutrition story doing rounds on the internet. It suggests a 180-degree turn on how to deal with rising incidence of peanut allergies. Instead of keeping infants away from nuts, it urges parents to incorporate them into early, and often. I haven't looked at the original study carefully, but my instincts on retractions and reversals of consensus tells me to take the findings seriously.

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