Whatever the precise non-publication rate is, it is a serious waste of the roughly $180 billion annually invested in health and medical research globally
If 50% of mail we posted never arrived, the outcry would be considerable. Although current estimates are that about half of research goes unpublished, there is little outcry. Maybe that is because the results of research projects are not addressed to a specific person who would notice when they hadn’t arrived; or maybe some think the situation isn’t as bad as implied by the 50% estimate.
Rates of publication have been documented best for clinical trials, particularly since trial registration at inception became more widespread over the past 20 years. In the 1980s and 1990s estimates of trial publication rates were derived from retrospective cohort studies of trial proposals submitted to ethics committees, and from specialist trial registers. In this century, however, mandated trials registration has enabled much larger cohorts of trials to be investigated.