Nearly half (47%) of all clinical trials remain unpublished.

Whether a trial is published and how long it takes is influenced by whether there are positive results, how large the trial is and if it is single- or multi-centred, and which type of organisation has funded the trial.

Publication bias is a problem because it means that the information available to people making important health-related decisions for themselves, their relatives or their patients is not complete and may even be misleading. For example, if negative results have not been published, there is a danger that the decision-makers may not be aware of possible harms linked to the intervention.