Table 2

Characteristics of all interventional clinical trials on the International Clinical Trials Registry Platform (ICTRP) registered from 2005 to 2013 (N=173 532)

CategoryNumber of trials registered from 2005–2013Percentage of all clinical trials registered from 2005–2013 (%)
Region (income groups)*
 High-income countries143 13782.5
 Upper middle-income countries24 93714.4
 Lower middle-income countries82294.7
 Low-income countries14330.8
 Not specified63193.6
Region (geographical)*
 Northern America61 17035.2
 Europe61 11535.2
 Asia43 36425.0
 Oceania10 4326.0
 Latin America and the Caribbean74764.3
 Not specified62113.6
Registry name*,
 ClinicalTrials.gov119 04668.6
 EU-CTR21 26812.3
 JPRN11 2516.5
Study phase
 I16 1019.3
 I and II54783.2
 II22 61613.0
 II and III30621.8
 III17 46910.1
 III and IV1550.1
 IV15 1808.7
 Not specified92 54553.3
Target sample size
 10–9987 65350.5
 100–99961 93835.7
 10 000 –99 9996220.4
 100 000 or more770.0
 Not specified12 0376.9
Total per category173 532100
  • *Overlap was possible, total in this category was greater than 100%. Trials regularly recruit participants in multiple regions, and trials are often registered at more than one registry.

  • †Registry acronyms stand for: EU Clinical Trials Register (EU-CTR), Japan Primary Registries Network (JPRN), International Standard Randomized Controlled Trial Number Register (ISRCTN), Australian New Zealand Clinical Trials Registry (ANZCTR), Iranian Registry of Clinical Trials (IRCT), The Netherlands National Trial Register (NTR), Clinical Trials Registry—India (CTRI), Chinese Clinical Trial Register (ChiCTR), German Clinical Trials Register (DRKS), Clinical Research Information Service (CRiS) Republic of Korea, Brazilian Clinical Trials Registry (ReBEC), Pan African Clinical Trial Registry (PACTR), Cuban Public Registry of Clinical Trials (RPCEC), Sri Lanka Clinical Trials Registry (SLCTR), and Thai Clinical Trials Registry (TCTR). For CTRI and JPRN precise data on the annual number of registered interventional clinical trials could not be acquired; data were approximated from the overall number of studies (interventional and observational) on these registries’ websites and the distribution of interventional and observational trials from these registries on the ICTRP.