Related Experiment Video
Updated: May 19, 2026
Inverse Probability of Treatment Weighting (Propensity Score) using the Military Health System Data Repository and National Death Index
Published on: January 8, 2020
Identification of additional trials in prospective trial registers for Cochrane systematic reviews
Wynanda A van Enst1, Rob J P M Scholten, Lotty Hooft
1Dutch Cochrane Centre, Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical Center, Amsterdam, The Netherlands. w.a.vanenst@amc.uva.nl
Background:
Publication and selective outcome reporting bias are a threat to the validity of systematic reviews. Extensive searching for additional trials in prospective trial registers could reduce this problem. We have evaluated how authors of Cochrane systematic reviews currently make use of trial registers as an additional source for the identification of potentially eligible trials.
Methodology/Principal Findings:
We included 210 systematic Cochrane reviews of interventions published between 2008 and 2010 of which the protocol was first published in 2008. When prospective trial registers were searched we recorded the names of the register(s), the authors' motive(s) and if they yielded any extra trials. In 80 reviews (38.1%) the authors had searched in one or more prospective trial register(s) of which 55% had searched in overlapping search portals and individual registers. Most frequently assessed were the MetaRegister (66.3%) and Clinicaltrials.gov (60%) which is in sharp contrast of other registers or portals like the WHO ICTRP Search Portal (20%). Reported motives to use registers were to identify ongoing trials (83.3%), to identify unpublished outcomes or trials (23.5%), to identify recently published trials (11.8%), or to identify any relevant trial (3.9%).In 28 reviews (35%) the authors had selected (ongoing) trials identified in trial registers as potentially eligible.
Discussion:
Trial registers as an additional source of information are gaining acknowledgement amongst Cochrane reviewers. Nevertheless, searches seem to be inefficient as overlapping databases are frequently consulted, while the WHO ICTRP Search Portal that includes the data from all approved registers worldwide is being underused. Moreover, the emphasis is now on the identification of ongoing trials, although the prospective registers offer a broader potential. Further familiarity of registers and guidance how to search and to report will help to implement this as a common method and utilize the full potential of prospective trial registers for systematic reviews.
Insights
Cochrane reviewers increasingly use trial registers to find studies, but searches are often inefficient. Underutilization of comprehensive portals like WHO ICTRP limits the potential of trial registers in systematic reviews.
Area of Science:
- Medical Research Methodology
- Evidence Synthesis
- Clinical Trial Management
Background:
- Publication bias and selective outcome reporting threaten systematic review validity.
- Prospective trial registers can mitigate these biases by enabling extensive trial searching.
- This study assesses the current use of trial registers by Cochrane systematic review authors.
Purpose of the Study:
- To evaluate how Cochrane systematic review authors utilize trial registers for identifying eligible trials.
- To understand the motives and effectiveness of using trial registers in systematic reviews.
Main Methods:
- Analysis of 210 Cochrane systematic reviews published between 2008-2010 with protocols from 2008.
- Recorded register names, author motives, and identification of extra trials.
- Assessed frequency of use for specific registers and portals.
Main Results:
- 38.1% of reviews searched trial registers; 55% used overlapping databases.
- MetaRegister (66.3%) and ClinicalTrials.gov (60%) were most common; WHO ICTRP Search Portal was underused (20%).
- Primary motive was identifying ongoing trials (83.3%); 35% selected trials from registers as eligible.
Conclusions:
- Trial registers are gaining traction in systematic reviews, but current search strategies are inefficient.
- Underutilization of comprehensive resources like WHO ICTRP limits potential benefits.
- Improved familiarity and guidance are needed to fully leverage trial registers for robust systematic reviews.
Related Concept Videos
01:16Clinical Trials
There are four phases in a clinical trial. A phase one...
01:11Clinical Trials: Overview
01:11Observational Studies
There are three types of observational studies – Prospective, retrospective, and cross-sectional.
Prospective Study
Prospective studies, also known as longitudinal or cohort studies, are carried out by collecting future data from groups sharing similar characteristics. One example of...
01:20Study Designs in Epidemiology
Observational studies are those where the researcher does not intervene but rather observes natural variations. They include cross-sectional, cohort, and case-control studies.
01:23Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast, controlled...
01:16Crossover Experiments
Crossover designs are performed even with smaller sample sizes since the samples can act as their controls. These are better than simple randomized trials since patients are exposed to all the treatments.