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The Cochrane Library (named after Archie Cochrane) is a collection of databases in medicine and other healthcare specialties provided by Cochrane and other organizations. At its core is the collection of Cochrane Reviews, a database of systematic reviews and meta-analyses that summarize and interpret the results of medical research. The Cochrane Library aims to make the results of well-conducted clinical trials readily available and is a key resource in evidence-based medicine.
A hierarchy of evidence, comprising levels of evidence (LOEs), that is, evidence levels (ELs), is a heuristic used to rank the relative strength of results obtained from experimental research, especially medical research. There is broad agreement on the relative strength of large-scale, epidemiological studies. More than 80 different hierarchies have been proposed for assessing medical evidence. The design of the study (such as a case report for an individual patient or a blinded randomized controlled trial) and the endpoints measured (such as survival or quality of life) affect the strength of the evidence. In clinical research, the best evidence for treatment efficacy is mainly from meta-analyses of randomized controlled trials (RCTs) and the least relevant evidence is expert opinion, including consensus of such. Systematic reviews of completed, high-quality randomized controlled trials â such as those published by the Cochrane Collaboration â rank the same as systematic review of completed high-quality observational studies in regard to the study of side effects. Evidence hierarchies are often applied in evidence-based practices and are integral to evidence-based medicine (EBM).
Water fluoridation is the controlled addition of fluoride to public water supplies to reduce tooth decay. Fluoridated water maintains fluoride levels effective for cavity prevention, achieved naturally or through supplementation. In the mouth, fluoride slows tooth enamel demineralization and enhances remineralization in early-stage cavities. Defluoridation is necessary when natural fluoride exceeds recommended limits. The World Health Organization (WHO) recommends fluoride levels of 0.5â1.5Â mg/L, depending on climate and other factors. In the U.S., the recommended level has been 0.7Â mg/L since 2015, lowered from 1.2Â mg/L. Bottled water often has unknown fluoride levels.
Tooth decay affects 60â90% of schoolchildren worldwide. Fluoridation reduces cavities in children, with Cochrane reviews estimating reductions of 35% in baby teeth and 26% in permanent teeth when no other fluoride sources are available, though efficacy in adults is less clear. In Europe and other regions, declining decay rates are attributed to topical fluorides and alternatives like salt fluoridation and nano-hydroxyapatite.