Table 2 Characteristics of unpublished trials with and without results available in the ClinicalTrials.gov results database. Values are numbers (percentages) unless stated otherwise

Trial characteristicsResults in ClinicalTrials.gov
Available (n=38)Not available (n=133)
Mean (SD) No of participants1199 (1049)1911 (10 244)
Trial phase*:
 I/II5 (13)36 (27)
 III24 (63)80 (60)
 IV8 (21)10 (8)
 Other1 (3)7 (5)
Funding source†:
 Industry38 (100)112 (84)
 NIH/US government0 (0)11 (8)
 Other0 (0)20 (15)
Trial completion date:
 Unlisted0 (0)18 (11)
 Prior to 20050 (0)3 (2)
 2005-063 (8)19 (14)
 20075 (13)50 (38)
 200830 (79)43 (32)

NIH=National Institutes of Health.

*Trials described as “phase II/III” in their registry entry are categorized as phase III.

†Trials with multiple funding sources are listed within all relevant categories; totals therefore add to more than 100%.