An introduction to Evidence Based Medicine

What do you mean by evidence-based medicine?  Whilst the term evidence based medicine (EBM) is probably familiar to most readers, it is worth pausing initially to think about what we understand by the term. The claim that a position is "evidence based" can be used to try to silence any questions or argument. On the contrary, asking questions about the evidence for any suggested course of action is at the heart of EBM philosophy. I can do no better than to quote the introduction to one of my favourite books in this area, Follies and Fallacies in Medicine(1), in which the authors describe themselves as suffering from incurable "scepticaemia".

The first step towards using EBM to inform our daily practice is to be prepared to question whether we always know the best course of action or have looked at the evidence that underpins the decisions that we make.

We are certainly influenced by our own past experience, what our colleagues do and what experts tell us. These often enlighten us and inform our practice, but we must also be aware that experiences are subject to chance variation, and that the person who is closest at hand may not give the best advice. For example, the experience of the last patient with a condition is not necessarily the best pointer for the next one. What we were taught in medical school may also now be out of date. We do well, however, to remember that our own experience and those of our patients are always important and worth exploring. How many times have you had the experience of suddenly understanding why a patient has presented with a longstanding headache when they let slip that a friend at work had been diagnosed as having a brain tumour?

What EBM is not
Whilst it is invaluable to know what the evidence is in relation to problems that we have to investigate and treat, you may be surprised to learn that the advocates of EBM would be the first to agree that evidence is only a small part of making clinical decisions (see box).

Users Guides to the Medical Literature(2)

EBM is not a kind of cookbook medicine full of easy answers to difficult questions, and it can be quite time-consuming. In general as we dig into the evidence we find that there is much that is unknown, but tolerance of uncertainty is well known to us in primary care, and in my experience sharing this uncertainty carefully with patients is often surprisingly well received.

Why is EBM important?
There is an ever-increasing quantity of medical literature published each week and keeping up to date is a huge challenge. It is simply not possible to read all the relevant literature (even in our areas of special interest), so how can we stay in touch with recent developments? If you have written a personal learning plan I wonder whether this is a recognised problem and how you plan to address it?

Increasingly we are put under pressure by patients who have read about a new treatment in the paper or found an article on the Internet, or by consultants who advocate particular referral or treatment pathways for patients with particular symptom presentations. So how are we to respond?

The medical literature is a powerful resource for us, but we have to recognise that it serves many different needs. Those who commission and carry out medical research need somewhere to publish the findings of their work. This may be of high or low quality, and it is not necessarily safe to assume that publication of a paper in a peer-review journal means you can believe all that the authors say. Just look at the subsequent correspondence if you want to see what I mean!

The bottom line is whether this paper means that I should change what I am currently doing, and in order to assess this some basic skills are needed. Many of these, including some explanation of statistical concepts, will be covered in later articles in this series, but the first useful skill is being able to turn a vague concern into an answerable question.
We need to be able to pose a question that reliable research studies can answer. The structure of such a question in relation to treatment options will have 4 parts to it and can be summarised using the acronym PICO. We need to consider the Patient's problem, the Intervention suggested, the possible Comparative treatments and the Outcomes that matter (see Box).


Thus "Does my child need antibiotics for this ear infection?" might be rephrased "In children with acute otitis media, how much difference do antibiotics make in comparison with paracetamol alone, in terms of duration of pain, deafness, recurrent infections and serious complications".

Once we have determined the question that we want to ask, we can move on to decide what is the most valid evidence to answer the question and how to find it.
Archie Cochrane's Challenge
I was impressed as a student by Archie Cochrane's book 'Effectiveness and Efficiency' in which he pointed out that we could be as efficient as we like in providing medical care, but that if it is not effective care we are wasting our time(3). He set out a challenge in 1979 as follows(4):

In response to this challenge the Cochrane Collaboration prepares and updates such summaries in the form of systematic reviews of the best evidence available, and there are now over 1,000 of these on the Cochrane Library. Whilst there will inevitably be gaps in this database for some time to come, increasing numbers of reviews do address issues related to primary care.
I would be the first to admit that Cochrane reviews are not light reading, but a later article in this series will address the subject of how to understand systematic reviews. Moreover part of the purpose of publications such as Clinical Evidence is to summarise the results of Cochrane reviews in a concise understandable format.

EBM in daily practice
If we want to practice better medicine we will need to keep up to date with new developments and decide how to integrate them into our practice. The concept of Clinical Governance challenges us to demonstrate whether we have been able to measure changes in our practice as a result. This can be challenging and exciting but we have to be realistic about how much can be achieved in the face of numerous demands made upon us and the volume of uncertainties that we face every day. We also need to avoid efficiently implementing treatments that are not effective!

There is little point wasting time looking for answers that probably do not exist, and in my experience the quickest place to start looking is in a synopsis of published research that has already been assessed for quality, such as Clinical Evidence or Best Evidence (an electronic summary of Evidence Based Medicine Journal and ACP Journal Club). Whilst searching Medline may be more familiar the best data tends to be buried in a sea of other material. Again this will be dealt with in more depth in a future article.

So if all this sounds like hard work – it is! But it is worth it and it can be fun, so look out for the future topics in this series that may change the way you read journals and perhaps even how you practise in the future.


References
1. Skrabanek P, McCormick J. Follies and Fallacies in Medicine. 3 ed: Tarragon Press; 1998.
2. Guyatt G, Rennie D. Users' Guides to the Medical Literature: AMA Press; 2001.
3. Cochrane A. Effectiveness and Efficiency: The Nuffield Provincial Hospitals Trust; 1971.
4. Cochrane A. 1931-1971: a critical review, with particular reference to the medical profession. In: Medicine for the year 2000. London: Office of Health Economics; 1979. p. 1-11.

Reproduced with permission.  Complete series available from the Prescriber website