Mức độ bằng chứng Trong thời đại y học dựa trên bằng chứng, cần phải có một phương pháp phân loại các bằng chứng sẵn có để cho biết nó hữu ích như thế nào. Hệ thống sau đây là một trong những được sử dụng bởi Viện Y tế và Lâm sàng Quốc gia Anh (NICE). Các tổ chức khác sản xuất hướng dẫn có thể sử dụng hệ thống hơi khác nhau | Evidence-based medicine Evidence-based medicine The use of current best evidence clinical expertise and patient values to make decisions about the care of individual patients. Levels of evidence In this era of evidence-based medicine there needs to be a method of categorizing the available evidence to indicate how useful it is. The following system is the one used by the UK National Institute for Health and Clinical Excellence NICE . Other organizations that produce guidelines may use slightly different systems but the hierarchy of usefulness remains the same. The levels of evidence are based on study design with some systems such as this one subdividing the grades further depending on the methodological quality of individual studies. Level Evidence description 1a Systematic review or meta-analysis of one or more randomized controlled trials RCT 1b At least one RCT 2a At least one well-designed controlled non-randomized study 2b At least one well-designed quasi-experimental study for example a cohort study 3 Well-designed non-experimental descriptive studies for example comparative correlation or case-control studies or case series 4 Expert opinion Grade of recommendations Similarly the strength of any recommendation made on the basis of the evidence can be categorized. This is an example from NICE. Grade Recommendation description A Based directly on level 1 evidence B Based directly on level 2 evidence or extrapolated from level 1 evidence C Based directly on level 3 evidence or extrapolated from level 1 or level 2 evidence D Based directly on level 4 evidence or extrapolated from level 1 level 2 or level 3 evidence GPP Good practice point based on the view of the Guideline Development Group Evidence-based medicine 221 An alternative is to think in terms of do it or don t do it based on conclusions drawn from high-quality evidence or probably do it or probably don t do it based on moderate quality evidence. Low-quality evidence leads to uncertainly and inability
