Living Evidence Syntheses in Practice: Methodology, Standards, dissemination and publication challenges.Paper 1: Introduction - Are Living Evidence Syntheses Truly 'Living'?

BACKGROUND: This first paper in the Living Evidence Synthesis in Practice series examines how living evidence syntheses (LES) have been defined, implemented, reported, and updated over time. It introduces key concepts of living evidence and describes the characteristics of baseline syntheses and subsequent updates, focusing on question types, methodological features, and update trends. METHODS: We conducted a methodological survey of LES, defined as evidence synthesis products (e.g., systematic reviews, meta-analyses, network meta-analyses, rapid reviews, and overviews of reviews) that explicitly adopted a living evidence approach. An LES was defined as comprising a baseline synthesis report (BSR) and subsequent update reports (UDRs) and/or evidence surveillance reports (ESRs). Eligible LES were identified through comprehensive searches of the Epistemonikos database, grey literature, and organizational repositories. Identified LES were prospectively tracked from March 2022 to January 2025. Data were extracted independently in duplicate using a standardized form and analyzed descriptively to characterize baseline features, update patterns, and methodological practices over time. RESULTS: Searches conducted up to March 2022 identified 1,730 records, with 28 additional records located through manual searches. After screening and linking related references, 119 LES were included. All LES were monitored for two years to identify further updates. By January 2025, 123 additional reports had been identified, yielding a final dataset of 119 BSRs, 160 UDRs, and 41 ESRs. Overall, 49 LES (41.2%) produced at least one UDR or ESR during follow-up. The median number of updates per LES was 1 for UDRs (IQR 1-4) and 3 for ESRs (IQR 2-8); only three LES (2.5%) produced both. Most baseline syntheses addressed intervention questions (64.7%), followed by prognosis (12.6%), epidemiology (12.6%), and diagnosis (9.2%). Most were labelled as living systematic reviews or living meta-analyses (86.6%), but only 32 (26.9%) cited references supporting the living approach. CONCLUSIONS: The living evidence approach is increasingly used, particularly for intervention questions. However, maintaining and consistently reporting these reviews remains challenging, as fewer than half were updated over two years. Stronger methodological and reporting standards are needed to ensure LES remain current, credible, and useful for decision-making. PLAIN LANGUAGE SUMMARY: Living evidence syntheses (LES) are secondary research studies designed to stay continuously up to date as new information becomes available. This type of review became especially popular during the COVID-19 pandemic, when health recommendations needed to change quickly based on new research. To better understand how LES are developed and maintained in the real world, we carried out a methodological study that tracked these reviews over a two-year period. We started by identifying all available LES published up to March 2022 using Epistemonikos database, as well as additional manual searches and author contacts. After we found the eligible LES, we carefully followed each one to see if, how, and when they were updated. In total, we included 119 baseline reviews and 201 related updates, forming a sample of 320 references. Most of these were standard systematic reviews, and nearly three-quarters were published in peer-reviewed journals. However, we found that less than half of the reviews were actually updated after they were first published. Many reviews that were meant to be "living" eventually stopped updating, sometimes without explanation. Our findings show that while the idea of living evidence is promising, putting it into practice is not always easy. There are clear benefits to keeping reviews current, but researchers need better tools, clearer guidelines, and more consistent publishing practices to help them maintain truly "living" reviews. This would ensure that health professionals and policymakers always have access to the most up-to-date and reliable information.