Indication bias or protopathic bias

In their article, Daniels and colleagues describe how the association between NSAID use and spontaneous abortions can be biased by the fact that NSAIDs could be taken to relieve the pain due to early symptons of the spontaneous abortion itself 1. The term ‘indication bias’ is used to define this bias but many readers may have been surprised not to find the term ‘protopathic bias’.