Reporting and identification of trial registration details in RCTs (n=188)
| Registration details | RCTs, n (%) |
| Reporting of registration number (n=188) | |
| Reported in primary study report* | 165 (88%) |
| Not reported in primary study report* | 17 (9%) |
| Registrations identified by active search/author request | 5 |
| No registration identified | 12 |
| Not published, only registration record available as primary study report* | 6 (3%) |
| Number of registrations per RCT (n = 176†) | |
| One registration record | 116 (66%) |
| Two registration records | 49 (28%) |
| Only one registration number reported in the publication (second identified by active search) | 36 |
| All reported in the publication | 13 |
| ≥ 3 registration records | 11 (6%) |
| Only up to two registration numbers reported in the publication (third identified by active search) | 9 |
| All reported in the publication | 2 |
| Registry (location) (n = 249‡) | |
| ClinicalTrials.gov (USA, international) | 142 |
| EUCTR (European Union) | 56 |
| ISRCTN (UK, international) | 15 |
| IRCT (Iran) | 12 |
| ChiCTR (China) | 9 |
| CTRI (India) | 6 |
| ReBEC (Brazil) | 5 |
| REec (Spain) | 2 |
| INA (Indonesia) | 1 |
| SCTR (Saudi Arabia) | 1 |
*Primary study report=publication/preprint or registration record, if RCT unpublished.
†Registrations identified via publication, active search or author request.
‡The number of registrations exceeds the total number of RCTs due to multiple registrations per RCT. We identified a total number of 249 on 176 RCTs.
ChiCTR, Chinese Clinical Study Register; CTRI, Clinical Trials Registry India; EUCTR, EU Clinical Trials Register; INA, Indonesia Clinical Research Registry; IRCT, Iranian Registry of Clinical Trials; ISRCTN, International Standard Randomised Controlled Trial Number; RCTs, randomised controlled trials; ReBec, Brazilian Registry of Clinical Trials; REec, Spanish Clinical Study Registry [Registro Español de Estudios Clínicos]; SCTR, Saudi Clinical Study Registry.