WASHINGTON, D.C. — Most clinical trials for cancer, heart disease and mental health are too small to offer adequate medical evidence, said a review of the US database of such studies released on Tuesday.

The analysis in the Journal of the American Medical Association was led by experts at Duke University in collaboration with the US Food and Drug Administration.

That partnership, known as the Clinical Trials Transformation Initiative (CTTI), examined more than 96,000 studies registered as of September 2010 with the website ClinicalTrials.gov, a US registry that was started in 1997.

In 2007, the registry became mandatory for most mid- to late phase interventional drug and device trials and study authors are now required by law to record key data elements, report basic results and adverse events.

The studies chosen for review were in ‘intervention medicine,