Many Large Clinical Trials Have Gone Missing

In medicine, we depend on the medical literature. However, what we cannot see — what is missing from the literature — might also be important. In the last decade, many studies have revealed that scientists conducting clinical trials too commonly do not provide the results publicly. Although some experts have suggested that trials with unreported data are mostly inconsequential, others have provided data that cast doubt on that belief.

To explore this issue further, Tatsioni and colleagues started with a search on ClinicalTrials.gov for long-unpublished, large, randomized trials that started after June 1, 2007, and were completed before June 1, 2012; the authors focused on the 500 trials with the largest number of participants. Trials for whi…