A German institute that evaluates the harms and benefits of drugs and other medical interventions says reliable assessments will never be possible without complete clinical trials data being made public.

Beate Wieseler, head of the drug assessment department at the German Institute for Quality and Efficiency in Health Care, says that the some of the data “would probably shed a totally new light on several drugs and their position in their therapeutic area.”

The call adds to a growing chorus of voices calling for more complete and transparent sharing of trials data as healthcare costs rise, payers fret over wasting money on potentially ineffective therapies, and researchers worry that information not shared publicly could leave information about a drug incomplete.

In an article published in the journal PLOS Medicine, institute researchers found that reporting of patient-relevant outcomes was far less complete in public sources than in clinical study reports provided privately to the institute by drugmakers. Additionally, they found there was considerably more information on harms in the private reports than in public sources.

The institute has joined a growing list of supporters, including the UK’s National Institute for Health and Clinical Excellence, in backing the AllTrials campaign, a push launched in January 2013 that calls for all past and present clinical trials to be registered and their results reported.

Researchers from the institute reported in a 2012 study that public information sources, such as scientific journals and entries posted in clinical trial registries alone, provided them with far less relevant information on methods and outcomes of clinical trials than non-public clinical study reports.

While the European Union’s chief drug regulator, the European Medicines Agency, plans to make public clinical trial data submitted with drug approval applications starting in 2014 (a policy being litigated), that move is not enough, the institute says. It wants to see companies legally required to share data from older trials too in order to support evaluation of drugs widely used in current medical practice.

Leaving the decision on what or what not to disclose up to each company is not a solution, says Wieseler. “A voluntary commitment by the pharmaceutical industry,” she says, “which would like to decide on a case-by-case basis which data it discloses, is insufficient.”