What is Evidence Based Medicine?

One definition would be: Delivery of Medical Care based on results of best available evidence. This usually means finding or relying upon data, some of which will be from outside one’s immediate memory to help answer a clinical question. EBM began to be championed by investigators, probably in the early 1990’s[1].

Studies that comprise the evidence are often in the form of Clinical trials. Clinical Trials are a relatively recent addition to the armamentarium of the tools available to clinicians – the first Randomized Clinical Trial (RCT) was done in 1952[2]. Trials should, but often don’t, look at how an innovation compares with prior knowledge, standards of care, or diagnostic accuracy. This is called comparative effectiveness (CE). In addition, trials often achieve “statistical significance”, which may, however, be of little pragmatic significance. The biological significance of much newer data is frequently incremental, not disruptive. Trials are almost never done to look at cost, although some report cost considerations in analyses that are done after the original publication. When cost does become a consideration, political or other influences challenge the focus or reduce funding of whoever is doing the research. For instance, the dissolution of the US OTA[3], which functioned from 1965 to 1995, is an example of outside influences resulting in the dissolution of a system that had worked to improve care in the 30 years the office was in existence.

When evaluating evidence one needs to be aware of at least three considerations/tests:

1. What is the source of the evidence (can you identify prospective biases, are the data reliable – Have non confirming data been looked for?)?
2. What is the Strength of any recommendations?
3. What is the Strength of the data that underlie the recommendations?

The AHA/ACC construct on strength of recommendations and the data supporting them is as good as any. Most other writing groups use some variations of those:

The strength of Recommendation is categorized as:

Class 1   Benefits Markedly Outweigh Risk, so the procedure/treatment should be done
Class IIa Benefits Somewhat Outweigh Risk, and it is reasonable to do the procedure/treatment
Class IIb Benefits May Equal or Minimally Outweigh Risk and it MAY be considered
Class III There is No Benefit or Harm may ensue. The procedure/treatment should generally be avoided unless there is a good reason to use it.

The Strength of the data is categorized as:

Level A Data are from multiple Randomized Clinical Trials (RCTs) or Meta-analyses
Level B Data are from limited populations (single RCT or non randomized studies)
Level C Consensus expert opinion, “standard of current care”, case studies.

There are two additional ways to look at EBM:

EBID – Evidence Based Individual Decision
EBG – Evidence Based Clinical Guidelines

Each has its place in the practice of EBM. In neither case should the evidence be looked at in isolation. New evidence should always be evaluated in the context of prior information, even though prior concepts may not be as soundly evidence based as newer information. The concept of Bayesian analysis where new evidence is evaluated based on prior heuristics should be applied. If new evidence comes about which markedly contradicts common or personal practice, the reliability of the source should be closely examined.

Guidelines are not new. One of the early guidelines was developed to help standardize and improve the diagnosis of Rheumatic Fever in 1944  – the Jones Criteria which were developed because, “From a study of the medical literature it is obvious that each observer has his (sic) own diagnostic criteria and these may differ widely”[4]. Thus, physicians couldn’t evaluate how therapies worked in this illness, because they didn’t really have a common definition of the illness. The guideline gave a way to be more confident of homogeneity in the diagnosis. The paper also allowed “clinical judgment” to override the criteria if done for good reason. CardioPulmonary Resuscitation was codified in 1966 because, “…clinical results vary widely and depend on the exact technique taught, the effectiveness of training…”[5]

Guidelines most often work for the majority of patients. When a patient or group of patients don’t respond to guideline based treatments, then a physician needs to determine why. Should the physician document that he/she has tried “standard or guideline recommended care” and that it hasn’t worked? How much should the patient know about a physician embarking on non-EBM care for this specific clinical condition? How much should the patient participate in any such “experiment” that such deviations from prior EBM/Guidelines represent? How much responsibility should the physician then have in sharing his/her observations with others? Alvin Feinstein in Clinical Judgment[6] discusses this concept.

Some Guidelines have multiple sources. Cardiac guidelines are often prepared with input from multiple physicians and other involved stakeholders from the ACC/AHA and the European Society of Cardiology. Some confusion may arise because there are “too many” guidelines. For heart failure, for example, there are FIVE distinct sets of guidelines, which are not concordant. Clearly for use by an individual or in groups, guidelines should be reviewed. For use by an institution or system a workable set should be developed.  This exercise often helps bring physician groups and practices together and helps them work better within an institution.

Some Sources of “Evidence”

Cochrane Collaboration
http://www.cochrane.org/

POEMS (Patient Oriented Evidence that Matters – Primary Care Oriented)
http://www.essentialevidenceplus.com/

USPSTF (United States Preventive Services Task Force)
http://www.ahrq.gov/clinic/uspstfix.htm

CADTH (Canadian Agency for Drugs and Technology in Health)
http://cadth.ca/

NICE (National Institute for Clinical Excellence – Great Britain)
http://www.nice.org.uk/

SBU (Swedish Council on Health Technology Assessment)
http://www.sbu.se/en/

Footnotes:

[1] McMaster EBM working group; Evidence Based Medicine: A new Approach to Teaching the Practice of Medicine; JAMA 1992, 268, 2420-5

[2] IOM (Institute of Medicine). 2011. Engineering a learning healthcare system: A look at the future: Workshop summary. Washington, DC: The National Academies Press

[3] OTA – Office of Technology Assessment: referred to in O’Donnell, JC et al: Health Technology Assessment: Lessons Learned from Around the World-An Overview: Value in Health, 2009, 12, Suppl. 2, S1-S5

[4] Jones, TD; The Diagnosis of Rheumatic Fever; JAMA, 1944, 126, 481-4

[5] Ad Hoc Committee on Cardiopulmonary Resuscitation … National Research Council: Cardiopulmonary Resuscitation; JAMA, 1966, 198, 138-145

[6] Feinstein, A; Clinical Judgment, 1967, Williams & Wilkins, Baltimore