What is Best Available Evidence?

Doctor Reading Articles

Every now and then I take questions I’ve answered in other venues, and copy the answers over here for posterity. This is one of those. While my job is now in Emerging Technologies, I have a long history working in evidence-based medicine and systematic review. I’m starting to feel like I’m choking with content in that area that I haven’t blogged, so I am going to start putting a few bits of it here from time to time.


I had a question about EBM. The definition of EBM is: “The best available research evidence means evidence from valid and practically relevant research, often from the basic sciences …”

So can we use just basic science to justify a treatment? Can anyone give an example please.


The definition I prefer is this, from David Sackett’s seminal article.

“Evidence based 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. By individual clinical expertise we mean the proficiency and judgment that individual clinicians acquire through clinical experience and clinical practice.”
David L Sackett, William M C Rosenberg, J A Muir Gray, R Brian Haynes, W Scott Richardson. Evidence based medicine: what it is and what it isn’t. BMJ 1996;312:71. http://www.bmj.com/content/312/7023/71.full

Or, even simpler, from the same work, “It’s about integrating individual clinical expertise and the best external evidence.”

Their section on the concept of “best available evidence” goes as follows.

“By best available external clinical evidence we mean clinically relevant research, often from the basic sciences of medicine, but especially from patient centred clinical research into the accuracy and precision of diagnostic tests (including the clinical examination), the power of prognostic markers, and the efficacy and safety of therapeutic, rehabilitative, and preventive regimens.”

My EBM / EBHC / EBD mentor and co-teacher, Amid Ismail, often made a big deal about this. The concept refers to the evidence pyramid, which you may have seen as an illustration around the EB literature. The version I use in teaching is on page two of this PDF:

CHAIN of TRUST: http://www-personal.umich.edu/~pfa/pro/courses/ChainOfTrustLoEVert2.pdf
Levels of Evidence, Updated for the Internet

Amid always emphasized that idea of best available evidence is ALWAYS tightly integrated with clinical judgment and the specific needs of the individual patient. So here is an example.


Let’s say there is a patient who is partially edentulous, struggling to eat, losing weight, becoming anorexic, and this is complicating other healthcare issues. The doctor wants to decide on the best way to make it easier for that patient to take in sufficient nutrition. The evidence base seems to suggest that dental implants are the best choice, and there are several systematic reviews in support of that concept. However, the patient has other conditions, of which the most important is rheumatoid arthritis (RA), and also has impaired wound healing. This makes the idea of surgeries for dental implants much more risky because of the patient’s personal situation. The RA also creates problems for the patient with using their hands, which might make for challenges managing post-operative care, which is a very important aspect of successful dental implants.

There are no systematic reviews on the population of partially-edentulous patients with RA, because the topic is too narrow and specific. Indeed, there are no articles at all on this combination of factors! This is no surprise, and is very common with rare conditions as well as less common combinations of conditions, often found among the elderly or persons with chronic health concerns. In this case, the best strategy for searching (and the best evidence) is likely to come from searching the major factors individually or in combination, then trying to integrate and weigh the evidence found to make a decision for that patient.

There is one article on the combination of partially edentulous and RA, based on a population of 6 patients.

Sato H, Fujii H, Takada H, Yamada N. The temporomandibular joint in rheumatoid arthritis–a comparative clinical and tomographic study pre- and post-prosthesis. J Oral Rehabil. 1990 Mar;17(2):165-72. http://www.ncbi.nlm.nih.gov/pubmed/2341957

That single article isn’t exactly on the topic we were searching, but it is as close to it as anything we can find. It recommends instead of implants to pull the teeth and place a prosthesis. Normally, according to the pyramid of evidence, this would not be evidence that ranks very highly. In this situation, it is the BEST evidence available.

The point is that for some questions or in some situations, the best evidence may not be very good; it might not be a systematic review, or an RCT, or even a case-controlled study. Sometimes it is a case report, or clinical experience. Sometimes it is animal studies, which we know don’t transfer over well to humans. A great deal of the research on dental implants comes in animal studies, so that might have happened with this question, if the complicating condition was perhaps diabetes or something other than RA. But a close match from an animal study compared with no evidence in humans means that the animal study is, for that question, the best evidence. It is not unusual for conditions that have a heavily immunological or microbiological aspect, for the emerging research to be based in labs, and may not have yet been tested in animals, much less people. Sometimes, in exceptional situations, especially if standard treatments have already failed, the best available evidence may even be personal reports. It is the clinician’s responsibility to examine the patient, gather the patient’s relevant history, review the evidence, select the best evidence, and integrate all of these in making a recommendation for a given patient. The point is not that the evidence is always excellent, but that it is, literally, the best available for that question and that patient.

One response to “What is Best Available Evidence?

  1. Pingback: Blog Index, January 27- February 17 | Emerging Technologies Librarian

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