Systematic reviews and meta-analyses that include registry-based studies: methodological challenges and areas for future research

Systematic reviews (SRs) are considered the highest level of evidence in various research areas, including medicine, social science, and economics. Traditionally, SR methods have been developed for trials and nonrandomized studies (e.g., cohort studies) that collect data to answer one or some defined research questions and not for studies that are based on routinely collected health care data like registries.