A guide to prospective meta-analysis

Background Following publication of the PRISMA statement, the UK Centre for Reviews and Dissemination (CRD) at the University of York in England began to develop an international prospective register of systematic reviews with health-related outcomes. The objectives were to reduce unplanned duplication of reviews and provide transparency in the review process, with the aim of minimizing reporting bias. Methods An international advisory group was formed and a consultation undertaken to establish the key items necessary for inclusion in the register and to gather views on various aspects of functionality. This article describes the development of the register, now called PROSPERO, and the process of registration. Results PROSPERO offers free registration and free public access to a unique prospective register of systematic reviews across all areas of health from all around the world. The dedicated web-based interface is electronically searchable and available to all prospective registrants. At the moment, inclusion in PROSPERO is restricted to systematic reviews of the effects of interventions and strategies to prevent, diagnose, treat, and monitor health conditions, for which there is a health-related outcome. Ideally, registration should take place before the researchers have started formal screening against inclusion criteria but reviews are eligible as long as they have not progressed beyond the point of completing data extraction. The required dataset captures the key attributes of review design as well as the administrative details necessary for registration. Submitted registration forms are checked against the scope for inclusion in PROSPERO and for clarity of content before being made publicly available on the register, rejected, or returned to the applicant for clarification. The public records include an audit trail of major changes to planned methods, details of when the review has been completed, and links to resulting publications when provided by the authors. Conclusions There has been international support and an enthusiastic response to the principle of prospective registration of protocols for systematic reviews and to the development of PROSPERO. In October 2011, PROSPERO contained 200 records of systematic reviews being undertaken in 26 countries around the world on a diverse range of interventions.

The reporting of outcomes within published randomized trials has previously been shown to be incomplete, biased and inconsistent with study protocols. We sought to determine whether outcome reporting bias would be present in a cohort of government-funded trials subjected to rigorous peer review. We compared protocols for randomized trials approved for funding by the Canadian Institutes of Health Research (formerly the Medical Research Council of Canada) from 1990 to 1998 with subsequent reports of the trials identified in journal publications. Characteristics of reported and unreported outcomes were recorded from the protocols and publications. Incompletely reported outcomes were defined as those with insufficient data provided in publications for inclusion in meta-analyses. An overall odds ratio measuring the association between completeness of reporting and statistical significance was calculated stratified by trial. Finally, primary outcomes specified in trial protocols were compared with those reported in publications. We identified 48 trials with 68 publications and 1402 outcomes. The median number of participants per trial was 299, and 44% of the trials were published in general medical journals. A median of 31% (10th-90th percentile range 5%-67%) of outcomes measured to assess the efficacy of an intervention (efficacy outcomes) and 59% (0%-100%) of those measured to assess the harm of an intervention (harm outcomes) per trial were incompletely reported. Statistically significant efficacy outcomes had a higher odds than nonsignificant efficacy outcomes of being fully reported (odds ratio 2.7; 95% confidence interval 1.5-5.0). Primary outcomes differed between protocols and publications for 40% of the trials. Selective reporting of outcomes frequently occurs in publications of high-quality government-funded trials.

There are potential benefits and harms of hyperoxemia and hypoxemia for extremely preterm infants receiving more vs less supplemental oxygen.