證據強度 Strength of Evidence @ 快樂小藥師

其實仔細找一下就會發現，這些證據強度的分類還有因為不同國家或是不同組織有不同的分法，所以簡單選一些常見的給大家參考：

Strength of Evidence

文獻依其研究架構，大致分成5 級實證醫學證據等級。

Level I：有顯著意義的隨機對照研究（Randomized controlled trials, RCT）報告。

Level II：世代研究（Cohort study）。

Level III：病例及對照組研究（Case-control study）。

Level IV：病例報告（Case series）。

LevelV：專家意見（Expert opinion）。

而當這些實證醫學文獻的證據等級應用在病人身上時，又可分成四個建議等級

（Grading system for recommendations），臨床上就可根據此建議等級，而形成臨床指引：

Group A：根據Level I 證據所做的建議。

Group B：根據Level II 證據所做的建議。

Group C：根據Level III 證據所做的建議。

Group D：根據Level III 以下等級證據所做的建議。

Grade	US Preventive Task Force	NHS R&D Center for EBM
A	This is good evidence to support the Recommendation	1a	SR of RCT (with narrow confidence interval)
		1b	individual RCT (with narrow confidence interval)
		1c	All-or-none studies
B	There is fair evidence to support the Recommendation	2a	SR of cohort studies ( with homogeneity )
		2b	individual cohort study or low-quality RCT(<80% follow up)
		2c	outcome research；Ecological studies
		3a	SR of case-control study
		3b	individual case-control study
C	There is insufficient evidence for or against, but recommendation may be made on other grounds	Case series and poor quality cohort/case-control Studies
D	There is fair evidence to exclude the Recommendation	Expert opinion without explicit critical appraisal, or based on bench research
E	There is good evidence to exclude the recommendation

RCT ：Randomized Control Trial（隨機臨床測試）

SR：Systematic Review

Oxford center for EBM (May 2001)

Grade	US Preventive Task Force	NHS R&D Center for EBM
A	This is good evidence to support the Recommendation	1a	整體隨意控制試驗(Total RCT)的系統性回顧(Systematic review)
		1b	個別隨意控制試驗(Individual RCT)
		1c	All-or-none studies
B	There is fair evidence to support the Recommendation	2a	整體相關病人研究(Cohort study)的系統性回顧
		2b	個別相關病人研究
		2c	指標結果(Outcome)研究
		3a	整體個案控制研究(Case-control study)的系統性回顧，
		3b	個別個案控制研究
C	There is insufficient evidence for or against, but recommendation may be made on other grounds	個案系列研究
D	There is fair evidence to exclude the Recommendation	未根據嚴格判斷的，或只根據生理或實驗研究的專家意見
E	There is good evidence to exclude the recommendation

在第二屆American Heart Association （AHA）International Evidence Evaluation Conference 以及the international Guidelines 2000 Conference on CPR and ECC,國際間專家的參與，大幅改變了未來的急救準則。未來的急救準則，必需要有國際性的實證醫學研究資料(evidence-based medicine)為基礎，才能達到應有的正確性及可信度。

2000 年指引會議是世界上第一次以國際性、科學性及證據為基礎之有關急救復甦的會議。所有指引皆經嚴密之審察，遵守實證醫學(evidence-based medicine)之原則。在指引後面之括弧內標有Class Ⅰ、Ⅱa、Ⅱb、Ⅲ及“尚待決定”之分級，這是表示過去實驗數據支持此指引之強度。

一般而言，各分級之意義如下：

證據等級	說明
Class I	表示在人體實驗上證明良好，確定有效之證據，並至少有一證據是前瞻性、隨機、控制下、正面效果的臨床試驗。
Class IIa	表示在人體實驗上是安全、有效。許多專家認為標示Class Ⅱa 的指引，非常值得推薦採用。
Class IIb	指證據力不及Ⅱa，但對人體無害。許多專家認為標示Ⅱb 之指引為可接受之替代方案。
尚待決定	證據不足以支持建議為臨床使用。通常這些指引尚在臨床嘗試階段，需要進一步再收集資料判斷。
Class III	表示沒有效用，但可能有害，因此不被接受。

Classification of recommendations:

Class I = conditions for which there is evidence and/or general agreement that a given procedure/therapy is beneficial, useful, and/or effective;

Class II = conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure/therapy;

Class IIa = weight of evidence/opinion is in favor of usefulness/efficacy;

Class IIb = usefulness/efficacy is less well established by evidence/opinion;

Class III = conditions for which there is evidence and/or general agreement that a procedure/therapy is not useful/effective and in some cases may be harmful.
^†Levels of evidence:

A = data are derived from multiple randomized clinical trials or meta-analyses;

B= data are derived from a single randomized trial or nonrandomized studies;

C = only consensus opinion of experts, case studies, or standard of care.

Systems to stratify evidence by quality have been developed, such as this one by the U.S. Preventive Services Task Force for ranking evidence about the effectiveness of treatments or screening:

Level I: Evidence obtained from at least one properly designed randomized controlled trial.
Level II-1: Evidence obtained from well-designed controlled trials without randomization.
Level II-2: Evidence obtained from well-designed cohort or case-control analytic studies, preferably from more than one center or research group.
Level II-3: Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled trials might also be regarded as this type of evidence.
Level III: Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.

The UK National Health Service uses a similar system with categories labeled A, B, C, and D. The above Levels are only appropriate for treatment or interventions; different types of research are required for assessing diagnostic accuracy or natural history and prognosis, and hence different "levels" are required. For example, the Oxford Centre for Evidence-based Medicine suggests levels of evidence (LOE) according to the study designs and critical appraisal of prevention, diagnosis, prognosis, therapy, and harm studies:

Level A: Consistent Randomised Controlled Clinical Trial, cohort study, all or none (see note below),clinical decision rule validated in different populations.
Level B: Consistent Retrospective Cohort, Exploratory Cohort, Ecological Study, Outcomes Research, case-control study; or extrapolations from level A studies.
Level C: Case-series study or extrapolations from level B studies.
Level D: Expert opinion without explicit critical appraisal, or based on physiology, bench research or first principles.

A newer system is by the Grade Working Group and takes in account more dimensions that just the quality of medical evidence. "Extrapolations" are where data is used in a situation which has potentially clinically important differences than the original study situation. Thus, the quality of evidence to support a clinical decision is a combination of the quality of research data and the clinical 'directness' of the data.

Despite the differences between systems, the purposes are the same: to guide users of clinical research information about which studies are likely to be most valid. However, the individual studies still require careful critical appraisal.

Note: The all or none principle is met when all patients died before the Rx became available, but some now survive on it; or when some patients died before the Rx became available, but none now die on it.

Categories of recommendations

In guidelines and other publications, recommendation for a clinical service is classified by the balance of risk versus benefit of the service and the level of evidence on which this information is based. The U.S. Preventive Services Task Force uses:

Level A: Good scientific evidence suggests that the benefits of the clinical service substantially outweighs the potential risks. Clinicians should discuss the service with eligible patients.
Level B: At least fair scientific evidence suggests that the benefits of the clinical service outweighs the potential risks. Clinicians should discuss the service with eligible patients.
Level C: At least fair scientific evidence suggests that there are benefits provided by the clinical service, but the balance between benefits and risks are too close for making general recommendations. Clinicians need not offer it unless there are individual considerations.
Level D: At least fair scientific evidence suggests that the risks of the clinical service outweighs potential benefits. Clinicians should not routinely offer the service to asymptomatic patients.
Level I: Scientific evidence is lacking, of poor quality, or conflicting, such that the risk versus benefit balance cannot be assessed. Clinicians should help patients understand the uncertainty surrounding the clinical service.

Task Force Ratings

Strength of Recommendations

The U.S. Preventive Services Task Force (USPSTF) grades its recommendations according to one of five classifications (A, B, C, D, I) reflecting the strength of evidence and magnitude of net benefit (benefits minus harms).

A.— The USPSTF strongly recommends that clinicians provide [the service] to eligible patients. The USPSTF found good evidence that [the service] improves important health outcomes and concludes that benefits substantially outweigh harms.

B.— The USPSTF recommends that clinicians provide [this service] to eligible patients. The USPSTF found at least fair evidence that [the service] improves important health outcomes and concludes that benefits outweigh harms.

C.— The USPSTF makes no recommendation for or against routine provision of [the service]. The USPSTF found at least fair evidence that [the service] can improve health outcomes but concludes that the balance of benefits and harms is too close to justify a general recommendation.

D.— The USPSTF recommends against routinely providing [the service] to asymptomatic patients. The USPSTF found at least fair evidence that [the service] is ineffective or that harms outweigh benefits.

I.— The USPSTF concludes that the evidence is insufficient to recommend for or against routinely providing [the service]. Evidence that the [service] is effective is lacking, of poor quality, or conflicting and the balance of benefits and harms cannot be determined.

Quality of Evidence

The USPSTF grades the quality of the overall evidence for a service on a 3-point scale (good, fair, poor):

Good: Evidence includes consistent results from well-designed, well-conducted studies in representative populations that directly assess effects on health outcomes.

Fair: Evidence is sufficient to determine effects on health outcomes, but the strength of the evidence is limited by the number, quality, or consistency of the individual studies, generalizability to routine practice, or indirect nature of the evidence on health outcomes.

Poor: Evidence is insufficient to assess the effects on health outcomes because of limited number or power of studies, important flaws in their design or conduct, gaps in the chain of evidence, or lack of information on important health outcomes.

GRADE working group

http://www.gradeworkinggroup.org/

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