From 【wiki】
最早1979年 “加拿大定期健康檢查工作隊”提出該標準【遞減】
I-Evidence?
Evidence from at least one?randomized controlled trial
至少有一個隨機對照試驗獲得的證據
II1-Evidence?
Evidence from at least one well designed?cohort study?or?case control study, i.e. a controlled trial which is not randomized
至少有一個合理設計的群組研究（cohort study）或者案例對照研究（case control study）, 即一個可控的非隨機對照試驗獲得的證據
II 2-Evidence
Comparisons between times and places with or without the intervention
進行過干預或非干預的比較研究，比較不同的時間和地點（的案例）獲得的證據
III-Evidence
Opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees.
來自于權威機構的觀點，基于臨床經驗、描述性研究或專家委員會的報告
加拿大定期健康檢查工作隊(CTF) 將他們的提議分為五分制，五檔：
A: Good level of evidence for the recommendation to consider a condition,
基于扎實的證據而提議考慮某情況
B: Fair level of evidence for the recommendation to consider a condition,?
基于合理的證據而提議考慮某情況
C: Poor level of evidence for the recommendation to consider a condition,?
基于較弱的證據而提議考慮某情況
D: Fair level evidence for the recommendation to exclude the condition,?
基于合理的證據而提議排除某情況
E: Good level of evidence for the recommendation to exclude condition from consideration.
基于扎實的證據而提議排除某情況
1988年美國預防服務工作隊（United States Preventive Services Task Force(USPSTF)）基于CTF 提出如下標準：
Level I:?
Evidence obtained from at least one properly designed?randomized controlled trial.
至少從一個合理設計的隨機對照試驗獲得的證據
Level II-1:?
Evidence obtained from well-designed controlled trials without?randomization.
從一個合理設計的非隨機的對照試驗獲得的證據
Level II-2:?
Evidence obtained from well-designed?cohort?or?case-control?analytic studies, preferably from more than one center or research group.
從一個合理設計的群組研究（cohort study）或者案例對照研究（case control study）獲得的證據, 最好來自多于一個研究中心或研究小組
Level II-3:?
Evidence obtained from multiple time series designs with or without the intervention. Dramatic results in uncontrolled trials might also be regarded as this type of evidence.
從多個干預或非干預的時間序列獲得的證據, 由于非控制而導致對照實驗產生劇烈的結果差異，也歸為此類
Level III:?
Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.
來自于權威機構的觀點，基于臨床經驗、描述性研究或專家委員會的報告
Another example of a system for grading evidence is the?Oxford (UK) CEBM Levels of Evidence, Most of the evidence ranking schemes grade evidence for therapy and prevention, but not for diagnostic tests, prognostic markers, or harm. The Oxford CEBM Levels of Evidence addresses this issue and provides 'Levels' of evidence for claims about prognosis, diagnosis, treatment benefits, treatment harms, and screening. The original CEBM Levels was first released in September 2000 for Evidence-Based On Call to make the process of finding evidence feasible and its results explicit. As published in 2009[9]they are?:
1a:
Systematic reviews?(with homogeneity) of randomized controlled trials
由隨機對照實驗得到的（同一主題的）綜合觀點
1b:?
Individual randomized controlled trials (with narrow?confidence interval)
單獨的隨機對照實驗（置信區(qū)間?。?/p>
1c:?
All or none randomized controlled trials
要么全部，要么沒有任何一個，是隨機對照實驗【我不太理解為什么全部的隨機對照實驗是1c】
2a:?
Systematic reviews (with homogeneity) of cohort studies
由群組研究得到的（同一主題的）綜合觀點
2b:?
Individual cohort study or low quality randomized controlled trials (e.g. <80% follow-up)
單獨的群組研究，或者質量較低的隨機對照實驗（比如小于80%后續(xù)實驗）【對于這個例子我并不理解】
2c:?
"Outcomes" Research; ecological studies
臨床實效研究；生態(tài)學研究
3a:?
Systematic review (with homogeneity) of case-control studies
由案例對比研究得到的（同一主題的）綜合觀點
3b:?
Individual case-control study
單獨的案例對比研究
4:
Case series?(and poor quality cohort and case-control studies)
病歷分析（也包括低質量的群組和案例對比研究）
5:
Expert opinion?without explicit critical appraisal, or based on physiology, bench research or "first principles"
無明確的批判性鑒定的專家意見，或基于生理學的實驗室研究或“第一原理（公理）”
In 2011, the Oxford CEBM Levels were redesigned by an international team to make it more understandable and to take into account recent developments in evidence ranking schemes. The Oxford CEBM Levels of Evidence have been used by patients, clinicians and also to develop clinical guidelines including recommendations for the optimal use of phototherapy and topical therapy in?psoriasis[10]?and guidelines for the use of the BCLC staging system for diagnosing and monitoring?hepatocellular carcinoma?in Canada.[11]
鏈接?en.wikipedia.org/wiki/Levels_of_evidence
en.wikipedia.org/wiki/Randomized_controlled_trial
隨機對照試驗（英語：randomized?controlled?trial，RCT）是一種對醫(yī)療衛(wèi)生服務中的某種療法或藥物的效果進行檢測的手段，特別常用于醫(yī)學、藥學、護理學研究中，在司法、教育、社會科學等其他領域也有所應用。
隨機對照試驗的基本方法是，將研究對象隨機分組，對不同組實施不同的干預，在這種嚴格的條件下對照效果的不同。在研究對象數量足夠的情況下，這種方法可以抵消已知和未知的混雜因素對各組的影響。
“臨床實效研究”或“實效研究”（Outcomes Research），也有人稱之為“效果研究”，是近年來在國際臨床醫(yī)學領域迅速發(fā)展起來的新學科。在許多臨床試驗（Clinical Trials）研究中，凡是有多種疾病、有多種并發(fā)癥或服用多種藥物的病人常常被排除在外。臨床實效研究則是研究藥物或其它醫(yī)療措施在非控制的真實臨床情況下（real world）的效果及經濟和社會效益等[1]。臨床試驗研究（如RCT）和實效研究對于充分了解一個醫(yī)療產品的實際醫(yī)療效果、效益和安全性有著同樣重要的意義，只是方法學上有所不同。
第一原理（英語：First principle），哲學與邏輯名詞，是一個最基本的命題或假設，不能被省略或刪除，也不能被違反。第一原理相當于是在數學中的公理。最早由亞里斯多德提出。
