循证医学第二讲

• Randomised controlled trials have drawbacks too. • External validity is one. This term indicates the extent to which results can be generalised to the broader community. • As with cohort studies, the randomised controlled trial can be prohibitively expensive.
2014/12/18
南通大学医学院
证据分级—概述
证据分类分级与推荐
耿劲松
医学院 医学信息学系 联系方式：13814606892 E-mail: gjs@
祈通中西 力求精进
证据帮助 时间和精力
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浩瀚的信息 高质量证据 决策者 证据生产者
一、证据分级
The Evidence Pyramid
循证医学 Evidence‐based Medicine
循证医学 Evidence‐based Medicine
Randomised controlled trial: gold standard
• The randomised controlled trial is the only known way to avoid selection and confounding biases in clinical research. • The hallmark of randomised controlled trials is assignment of participants to exposures purely by the play of chance. • When properly implemented, random allocation precludes selection bias. bias
循证医学 Evidence‐based Medicine
Rating clinical evidence
Assessment system of the US Preventive Services Task Force • I Evidence from at least one properly designed randomised controlled trial. • II-1 Evidence obtained from well-designed controlled trials without randomisation. • II-2 II 2 Evidence from well-designed well designed cohort or case-control case control studies studies, preferably from more than one centre or research group. • II-3 Evidence from multiple time series with or without the intervention. Important results in uncontrolled experiments could also be considered as this type of evidence. • III Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.
循证医学 Evidence‐based Medicine
循证医学 Evidence‐based Medicine
Cohort study: looking forward in time • Cohort studies proceed in a logical sequence: from exposure to outcome. • Recall bias is less of a concern than in the casecontrol study. • The cohort study enables calculation of true incidence rates, relative risks, and attributable risks.
循证医学 Evidence‐based Medicine
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A randomized controlled trial of the efficacy and safety of saxagliptin as add-on therapy in patients with type 2 diabetes and inadequate glycaemic control on metformin plus a sulphonylurea
循证医学 Evidence‐based Medicine
Strength of recommendations • A Good evidence to support the intervention. • B Fair evidence to support the intervention. • C Insufficient evidence to recommend for or against the intervention, but recommendation might be made on other grounds. • D Fair evidence against the intervention. • E Good evidence against the intervention.
Figure 2: Schematic diagram showing temporal direction of three study design
Grimes DA, Schulz KF. An overview of clinical research: the lay of the land. Lancet, 2002 , 359(9300):57-61
Non-randomised trial: penultimate design • Some experimental trials do not randomly allocate participants to exposures. • Advantages of a non-randomised trial include use of a concurrent control group and uniform ascertainment of outcomes for both groups. groups • However, selection bias can occur.
Diabetes Obes Metab. 2014, 16(5):443-450
• METHODS: In this 24-week, multicentre, randomized, parallel-group, double-blind study, outpatients aged ≥18 years with type 2 diabetes, body mass index ≤40 kg/m2 and inadequate glycaemic control, received saxagliptin 5 mg or placebo once-daily added to background medication consisting of a stable maximum tolerated dose of metformin plus a sulphonylurea. The primary end point was change in glycated haemoglobin (HbA1c) from baseline to week 24. Safety and tolerability assessments included adverse events (AEs), hypoglycaemia and body weight.
循证医学 Evidence‐8
Cross-sectional study: a snapshot in time • Sometimes termed a frequency survey or a prevalence study, cross-sectional studies are done to examine the presence or absence of disease and the presence or absence of an exposure at a particular time. p • Since both outcome and exposure are ascertained at the same time, the temporal relation between the two might be unclear.
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证据金字塔
2001年，美国纽约州立大学下州医学中心推出证据金字塔，首次将动 物研究和体外研究纳入证据分级系统，拓展了证据范畴，加之简洁明 了，形象直观，得到了非常广泛的传播。
Source: Guide to Research Methods: The Evidence Pyramid: </ebm/2100.htm>.
Case-control study: thinking backwards • Starting with an outcome, such as disease, this type of study looks backward in time for exposures that might have caused the outcome. • Case-control studies are especially useful for outcomes that are rare or that take a long time to develop, such as cardiovascular disease and cancer. • Recall bias (better recollection of exposures among the cases than among the controls) is a persistent difficulty in studies that rely on memory.