Table 1.

Characteristics of studies registered on the Clinicaltrials.gov website¹

Study characteristic	Number	%
Total studies registered in the USA	54890	100
Sex of study subjects
Females only	5314	9.7
Males only	2170	4.0
Both sexes combined	47355	86.3
Not indicated	51	<0.1
Age of study subjects
Adults (including seniors)	42283	77.0
Children	2952	5.4
Both adults and children	9646	17.6
Not indicated	9	<0.1
Study phase
Phase I	8145	14.8
Phase II	15911	29.0
Phase III	8142	14.8
Phase IV	4292	7.8
Phase not indicated	18400	33.5
Source of funding
Industry	15903	29.0
Non-industry*	32499	59.2
Blended (industry plus non-industry)	6477	11.8
Source of funding not indicated	11	<0.1

¹CTG began accepting trial registrations on 1 November 1999.

*The breakdown of non-industry-sponsored studies is as follows:

• 6480 trials for which NIH was the sole sponsor;
• 1227 trials sponsored by another US Federal agency;
• 10 166 trials with multiple non-industry sources of funding (including NIH); and
• 14 626 trials for which the funding source was listed as ‘other’ or was not listed.