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Levels of Evidence

The term Evidence-based Practice (EBP) is now being written in stone in the profession of physical therapy. Indeed, in his comments during the opening ceremony for the Annual Conference in June, 2005 the APTA President Ben Massey stated, “We have grown in our mastery of science and in our ability to use evidence to guide practice...” On the APTA website, the Advanced Clinical Practice course offerings are described as “Evidence-based, hands-on workshops for physical therapists only designed to advance clinical practice knowledge and skills.” The APTA has also developed the Hooked on Evidence program to provide a database of research evidence to support the tests, measurements, and interventions that are practiced everyday in physical therapy clinics. A quick internet search reveals textbooks and journal articles with the term evidencebased in the title. The listing of presentations at the Combined Sections Meeting and at Annual Conference also includes the qualifier evidencebased... in the title. Dr. David Sackett is the most cited proponent and author regarding the topic of evidence-based medicine (EBM). Indeed, almost every article written about EBM begins with a definition that was composed by him. It reads, “Evidencebased medicine is the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research.” Dr. Sackett and 4 of his colleagues simplified the definition in their well-known tutorial text on how to practice and teach EBM. They wrote, “Evidencebased medicine (EBM) is the integration of best research evidence with clinical expertise and patient values.” They also offered that, “New evidence from clinical research both invalidates previously accepted diagnostic tests and treatments and replaces them with new ones that are more powerful, more accurate, more efficacious, and safer.” Jules Rothstein gave an explanation regarding what constitutes evidence. He wrote, “...evidence is not faith or tradition. Evidence is viable findings from research, not theories underlying practice. Evidence is data that show whether treatments make a meaningful difference. Evidence is what is published in credible and respected journals.” However, Rennie cautioned readers of the literature not to automatically trust all that is published. He wrote that there is “... no study too fragmented, no hypothesis too trivial, no literature citation too biased or too egotistical, no design too warped, no methodology too bungled, no presentation of results too inaccurate and too contradictory, no analysis too selfserving, no argument too circular, no conclusion too trifling or too unjustified, and no grammar and syntax too offensive for a paper to end up in print.” As a professor I often emphasized to students to consider the recommendations of Crosby, Stills and Nash in the song they recorded titled, Wasted on the Way. I advised all my students to “... question all the answers...” The task of evaluating published research is daunting to many clinicians. To make the process easier, several scientists have outlined categories of evidence and stratified them in order from strongest to weakest levels. The levels also can be interpreted as starting with the most reliable or most trustworthy or the least vulnerable to bias, to the least trustworthy or the least reliable or the most vulnerable to bias. The levels of evidence outline by Sackett and his colleagues in 2000 are as follows: 1A = Systematic Review of Randomized Controlled Trials (RCTs) 1B = RCTs with Narrow Confidence Interval 1C = All or None Case Series 2A = Systematic Review Cohort Studies 2B = Cohort Study/Low Quality RCT 2C = Outcomes Research 3A = Systematic Review of Case-Controlled Studies 3B = Case-controlled Study 4 = Case Series, Poor Cohort Case Controlled 5 = Expert Opinion Hadorn and his colleagues outlined another way of classifying categories of evidence. These are the guidelines that were used to rate the quality of evidence that was used to create the Health Care Policy and Research Clinical Practice Guidelines. Only 3 levels are employed with this method. Level A = Well-conducted RCT with 100 patients or more (including multi-center and RESEARCH FORUM