Current trends in the application of causal inference methods to pooled longitudinal non-randomised data: a protocol for a methodological systematic review.

INTRODUCTION: Causal methods have been adopted and adapted across health disciplines, particularly for the analysis of single studies. However, the sample sizes necessary to best inform decision-making are often not attainable with single studies, making pooled individual-level data analysis invaluable for public health efforts. Researchers commonly implement causal methods prevailing in their home disciplines, and how these are selected, evaluated, implemented and reported may vary widely. To our knowledge, no article has yet evaluated trends in the implementation and reporting of causal methods in studies leveraging individual-level data pooled from several studies. We undertake this review to uncover patterns in the implementation and reporting of causal methods used across disciplines in research focused on health outcomes. We will investigate variations in methods to infer causality used across disciplines, time and geography and identify gaps in reporting of methods to inform the development of reporting standards and the conversation required to effect change. METHODS AND ANALYSIS: We will search four databases (EBSCO, Embase, PubMed, Web of Science) using a search strategy developed with librarians from three universities (Heidelberg University, Harvard University, and University of California, San Francisco). The search strategy includes terms such as 'pool*', 'harmoniz*', 'cohort*', 'observational', variations on 'individual-level data'. Four reviewers will independently screen articles using Covidence and extract data from included articles. The extracted data will be analysed descriptively in tables and graphically to reveal the pattern in methods implementation and reporting. This protocol has been registered with PROSPERO (CRD42020143148). ETHICS AND DISSEMINATION: No ethical approval was required as only publicly available data were used. The results will be submitted as a manuscript to a peer-reviewed journal, disseminated in conferences if relevant, and published as part of doctoral dissertations in Global Health at the Heidelberg University Hospital.

COVID-19 and Recreational Skiing: Results of a Rapid Systematic Review and Possible Preventive Measures.

COVID-19 is a novel infectious disease which has rapidly spread around the globe, disrupting several aspects of public life over the past year. After numerous infection clusters emerged among travelers hosted in ski resorts in early 2020, several European countries closed ski areas. These measures were mostly upheld throughout the 2020 and 2021 winter season, generating significant economic loss for mountain communities. The aim of this rapid systematic review was to explore the association between recreational skiing and the spread of COVID-19. This review was conducted according to the WHO practical guidelines on rapid reviews and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. PubMed, Scopus, MedRxiv and Promed-mail were screened to identify relevant scientific and grey literature published since the emergence of COVID-19. Among the 11 articles included, seven focused on cases recorded during the first epidemic wave, when COVID-19 containment measures were not yet mandatory. Most infection clusters could be directly linked to public gatherings which took place without the enforcement of restrictions. There is currently no evidence to suggest an association between COVID-19 spread and recreational skiing. It may be reasonable to consider the reopening of ski areas in compliance with strict rules and preventive measures.