group. Level II2: Comparisons between times and places with or without the intervention Level III: Opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees. The CTF graded their recommendations into a 5-point A–E scale: A: Good level of evidence for the recommendation to consider a condition, B: Fair level of evidence for the recommendation to consider a condition, C: Poor level of evidence for the recommendation to consider a condition, D: Fair level evidence for the recommendation to exclude the condition, and E: Good level of evidence for the recommendation to exclude condition from consideration. The CTF updated their report in 1984, in 1986 and 1987. United States In 1988, the United States Preventive Services Task Force (USPSTF) came out with its guidelines based on the CTF using the same 3 levels, further subdividing level II. 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 designs 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. Over the years many more grading systems have been described. United Kingdom In September 2000, the Oxford (UK) CEBM Levels of Evidence published its guidelines for 'Levels' of evidence regarding claims about prognosis, diagnosis, treatment benefits, treatment harms, and screening. It not only addressed therapy and prevention, but also diagnostic tests, prognostic markers, or harm. The original CEBM Levels was first released for Evidence-Based On Call to make the process of finding evidence feasible and its results explicit. As published in 2009 they are: 1a: Systematic reviews (with homogeneity) of randomized controlled trials 1b: Individual randomized controlled trials (with narrow confidence interval) 1c: All or none (when all patients died before the treatment became available, but some now survive on it; or when some patients died before the treatment became available, but none now die on it.) 2a: Systematic reviews (with homogeneity) of cohort studies 2b: Individual cohort study or low quality randomized controlled trials (e.g. <80% follow-up) 2c: "Outcomes" Research; ecological studies 3a: Systematic review (with homogeneity) of case-control