We used the WHO/ICRTP (ICTRP) Search Portal to identify a random sample of RCTs registered from January 1 to December 12, 2008 and open for recruitment on December 12, 2008. At the time of our study, the ICTRP Search Portal provided access to data from ClinicalTrials.gov and six WHO primary registries (Australian New Zealand Clinical Trials Registry (ANZCTR), the Chinese Clinical Trial Register, the Clinical Trials Registry - India, the German Clinical Trials Register, International Standard Randomised Controlled Trial Number Register (ISRCTN), and the Netherlands National Trial Register). Each record was screened by one reviewer (LR) to identify RCTs. The record was included if it explicitly used the word ‘random’ or variations thereof to describe the allocation method.
We extracted data on key methodologic items from each registry record using an evidence based source to define domains developed by the Cochrane Collaboration 
. The tool consists of six domains (sequence generation, allocation concealment, blinding, incomplete outcome data, selective outcome reporting and ‘other issues’) for assessing the quality of an RCT based primarily on published reports. The description of each domain provides a general risk of bias in the included randomized trials as well as any important flaws in the studies 
. Although some domains can only be evaluated once the trial is published, others are relevant at the registration stage and were designated as the primary outcomes of our study: the proportions of RCT records with adequate reporting of the methods of random sequence generation, allocation concealment, blinding and outcomes (primary, secondary, and harms outcomes). While harms can be primary or secondary outcomes, we decided to collect specific information on harms because they are frequently underreported. We also evaluated descriptions of the follow-up period, trial interventions and sample size calculations. For each methodological item, we defined adequate reporting based on the Cochrane Collaboration Risk of Bias tool 
, the Consolidated Standards of Reporting Trials (CONSORT) 
, the WHO Trial Registration Data Set (http://www.who.int/ictrp/network/trds/en/index.html
) and the instructions for registrants provided by registries (). An item was classified as inadequately reported if the reporting was unclear (i.e. some useful information provided, but insufficient detail to meet the definition of adequacy) or absent (i.e. no useful information provided) (). Finally, we also collected information on the type of intervention (drugs, procedures, behavior/education, devices, vaccines, and combined) and the type of funding (industry versus non-industry).
Criteria for defining adequate reporting.
The total number of records for all study designs is shown in . The ICTRP search portal does not differentiate records of RCTs from other study designs. We therefore estimated that 50% of these trial records were RCTs based on a random pilot sample of 100 records, as well an advanced search strategy using the word ‘random’ or variations thereof in the title or intervention field of all records from the ICTRP search portal. We sought to ensure adequate representation across registries by including all available RCTs from those registries with few records (the Chinese, Indian and German registries). For each of the other registries, we estimated the proportion of RCTs with adequate reporting of random sequence generation or allocation concealment to be less than 12% based on a pilot sample of 100 records. We then calculated the sample size required for each of these larger registries to yield an estimated prevalence of adequate reporting with 95% confidence, 80% power and 7% precision (). Each record in the sample was screened to ensure that it was an RCT (the word ‘random’ or variations thereof). For RCTs that were registered on multiple registries, we randomly selected only one record for inclusion.
Identification of study sample based on total number of recruiting studies and estimated number of RCTs registered from January 1 to December 12, 2008.
Two independent reviewers extracted information from each trial, with discrepancies resolved by discussion with a third evaluator. Five of the seven data extractors participated in an advanced method of systematic review course organized by the Ibero-American Cochrane Centre in Madrid and therefore received the same training on the Cochrane Collaboration Risk of Bias tool and other issues of RCT assessment. The two evaluators had experience in the used the Cochrane tool. Data were analyzed descriptively as weighted and raw proportions using SPSS 15.0, and Chi-square tests were used to determine associations between categorical variables.