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Background Stringent requirements exist regarding the transparency of the study selection process and the reliability of results. A 2-step selection process is generally recommended; this is conducted by 2 reviewers independently of each other (conventional double-screening). However, the approach is resource intensive, which can be a problem, as systematic reviews generally need to be completed within a defined period with a limited budget. The aim of the following methodological systematic review was to analyse the evidence available on whether single screening is equivalent to double screening in the screening process conducted in systematic reviews. Methods We searched Medline, PubMed and the Cochrane Methodology Register (last search 10/2018). We also used supplementary search techniques and sources (“similar articles” function in PubMed, conference abstracts and reference lists). We included all evaluations comparing single with double screening. Data were summarized in a structured, narrative way. Results The 4 evaluations included investigated a total of 23 single screenings (12 sets for screening involving 9 reviewers). The median proportion of missed studies was 5% (range 0 to 58%). The median proportion of missed studies was 3% for the 6 experienced reviewers (range: 0 to 21%) and 13% for the 3 reviewers with less experience (range: 0 to 58%). The impact of missing studies on the findings of meta-analyses had been reported in 2 evaluations for 7 single screenings including a total of 18,148 references. In 3 of these 7 single screenings – all conducted by the same reviewer (with less experience) – the findings would have changed substantially. The remaining 4 of these 7 screenings were conducted by experienced reviewers and the missing studies had no impact or a negligible on the findings of the meta-analyses. Conclusions Single screening of the titles and abstracts of studies retrieved in bibliographic searches is not equivalent to double screening, as substantially more studies are missed. However, in our opinion such an approach could still represent an appropriate methodological shortcut in rapid reviews, as long as it is conducted by an experienced reviewer. Further research on single screening is required, for instance, regarding factors influencing the number of studies missed.

Data Abstraction Assistant (DAA) is a software for linking items abstracted into a data collection form for a systematic review to their locations in a study report. We conducted a randomized cross-over trial that compared DAA-facilitated single-data abstraction plus verification (“DAA verification”), single data abstraction plus verification (“regular verification”), and independent dual data abstraction plus adjudication (“independent abstraction”). This study is an online randomized cross-over trial with 26 pairs of data abstractors. Each pair abstracted data from six articles, two per approach. Outcomes were the proportion of errors and time taken. Overall proportion of errors was 17% for DAA verification, 16% for regular verification, and 15% for independent abstraction. DAA verification was associated with higher odds of errors when compared with regular verification (adjusted odds ratio [OR] = 1.08; 95% confidence interval [CI]: 0.99–1.17) or independent abstraction (adjusted OR = 1.12; 95% CI: 1.03–1.22). For each article, DAA verification took 20 minutes (95% CI: 1–40) longer than regular verification, but 46 minutes (95% CI: 26 to 66) shorter than independent abstraction. Independent abstraction may only be necessary for complex data items. DAA provides an audit trail that is crucial for reproducible research.

Checklist items (table)7 for reporting an abstract of a randomised trial include: details of the trial's objectives; trial design (eg, method of allocation, blinding); participants in the trial (ie, description, numbers randomised and analysed); interventions intended for each randomised group and their effect on primary efficacy outcomes and harms; the trial's conclusions; the trial's registration name and number; and source of funding.

To determine the accuracy of single-reviewer screening in correctly classifying abstracts as relevant or irrelevant for literature reviews. We conducted a crowd-based, parallel-group randomized controlled trial. Using the Cochrane Crowd platform, we randomly assigned eligible participants to 100 abstracts each of a pharmacological or a public health topic. After completing a training exercise, participants screened abstracts online based on predefined inclusion and exclusion criteria. We calculated sensitivities and specificities of single- and dual-reviewer screening using two published systematic reviews as reference standards. Two hundred and eighty participants made 24,942 screening decisions on 2,000 randomly selected abstracts from the reference standard reviews. On average, each abstract was screened 12 times. Overall, single-reviewer abstract screening missed 13% of relevant studies (sensitivity: 86.6%; 95% confidence interval [CI], 80.6%–91.2%). By comparison, dual-reviewer abstract screening missed 3% of relevant studies (sensitivity: 97.5%; 95% CI, 95.1%–98.8%). The corresponding specificities were 79.2% (95% CI, 77.4%–80.9%) and 68.7% (95% CI, 66.4%–71.0%), respectively. Single-reviewer abstract screening does not appear to fulfill the high methodological standards that decisionmakers expect from systematic reviews. It may be a viable option for rapid reviews, which deliberately lower methodological standards to provide decision makers with accelerated evidence synthesis products.

We established a large database of trials to serve as a resource for future methodological and ethical analyses. Here, we use meta-data to describe the broad landscape of pragmatic trials including research areas, identification as pragmatic, quality of trial registry data and enrolment. Trials were identified by a validated search filter and included if a primary report of a health-related randomized trial published January 2014-April 2019. Data were collated from MEDLINE, Web of Science, ClinicalTrials.gov, and full text. 4337 eligible trials were identified from 13,065 records, of which 1988 were registered in ClinicalTrials.gov. Research areas were diverse, with the most common being general and internal medicine; public, environmental and occupational health; and health care sciences and services. The term “pragmatic” was seldom used in titles or abstracts. Several domains in ClinicalTrials.gov had questionable data quality. We estimated that one-fifth of trials under-accrued by at least 15%. There is a need to improve reporting of pragmatic trials and quality of trial registry data. Under accrual remains a challenge in pragmatic RCTs despite calls for more streamlined recruitment approaches. The diversity of pragmatic trials should be reflected in future ethical analyses.