A few people have asked us why we didn’t preregister the analysis for our potato diet study. We think this shows a certain kind of confusion about what preregistration is for, what science is all about, and why we ran the potato diet in the first place.
The early ancestor of preregistration was registration in medical trials, which was introduced to account for publication bias. People worried that if a medical study on a new treatment found that the treatment didn’t work, the results would get memory-holed (and they were probably right). Their fix was to make a registry of medical studies so people could tell which studies got finished as planned and which ones were MIA. In this sense, our original post announcing the potato diet was a registration, because it would have been obvious if we never posted a followup.
Pre-registration as we know it today was invented in response to the replication crisis. Starting around 2011, psychologists started noticing that big papers in their field didn’t replicate, and these uncomfortable observations slowly snowballed into a full-blown crisis (hence “replication crisis”).