Evidence-based medicine

Evidence Based Medicine (EBM) is the practice of using the best available evidence, gathered through research, to help make decisions about what treatments to give patients. It is easy to think that learning about EBM is a bit unnecessary. Obviously medicine is evidence based.

However, it is interesting to note that EBM has only been used in medicine since the 1970s. Before then, doctors would make decisions based on the experience they had from their years of working. This would involve making judgements based on what they were taught at medical school, what their colleagues used, and on what they’d read recently. Of course, scientific studies did exist at that time, but it was up to chance as to whether a doctor had read the latest studies, and which journals (where the evidence is published) they had looked at. As some of you will know, studies looking at how drugs work can give very different results, so which one do you believe?

All of this led to doctors prescribing very different medications for patients with the same health problems. Treatment was very subjective and, depending on how dedicated your doctor was, it could mean patients got very different standards of care. Indeed, many studies released around the 1960s and 70s revealed how variable the practice of medicine was and showed how damaging this was for patients. 1 The need for change became very clear and it was becoming plain how important EBM was.

How EBM changed medicine

Two important changes happened: The development of better trials, and the use of guidelines.

As mentioned above, different studies looking at how a medicine works can give different results. For example, a study may show that taking ‘Drug X’ each day adds 5 years to your life. Another may show it adds 10 years. Another one might say it reduces your life expectancy by 3 years. The reason for this is that there are lots of variables (factors that can change) when you complete a study. For example, the group of people you are giving ‘Drug X’ to, the amount of ‘Drug X’ you are giving, and the number of people in the study. A method was developed where studies looking at the same thing could be grouped together, their results compared and an ‘overall’ result given. This is called a ‘meta-analysis’. By doing this ‘combination’, you were able to get a more much more reliable idea of how effective a treatment really was.

Now that it was becoming clear which medicines were effective and which were not, the next step was to make sure doctors knew what the best treatment was, and when to use it. Doctors are busy, and do not have time to read all the latest research. Besides, even some meta-analyses can be poor quality. To resolve this, groups like NICE (the National Institute for Health and Care Excellence) were set up. Part of the role of NICE is to do all the ‘searching work’ for doctors. They analyse the evidence that is out there, apply rigorous standards as to what can and cannot be accepted, and come up with conclusions as to the best medication to give. These are written up and summarised into ‘guidelines’. These are very simple flow diagrams that tell the doctor what to do. Guidelines exist for thousands of conditions, from ‘simple’ health problems such as high blood pressure (hypertension), to emergency situations like advanced life support. 2 3 It would be useful to take a look at the NICE website to get an idea of what these guidelines entail.

Benefits of EBM

With a clear step-by-step structure for doctors to follow, and treatments with lots of evidence behind them, EBM led to vast improvements in the way patients were treated. There was less mortality (people dying from treatable conditions) and also less morbidity (long term side effects from having a condition). 4 This is a simple point to make, but it had a huge impact on how well people were cared for. As well as this treatment became fairer because, the national guidelines put in place meant you got the same treatment whether you lived in Southampton or the Shetland Islands,

Another benefit was that it made treatment more cost effective. The trials showed which medications were necessary and which were not, so doctors wouldn’t prescribe unnecessary drugs which increases cost and may potentially harm patients with side effects.

Problems with EBM

Some have argued that guidelines remove the ‘thinking’ aspect of medicine and make it much more robotic. All you have to do is work out the diagnosis, then give the first treatment on the guideline. If that doesn’t work, use the second one, and so on. Some people think this is a bit mindless, referring to it as practicing ‘medicine by numbers’. 5

There have also been questions about whether doctors using their intuition and subjectivity is actually all that bad. Having a ‘rule of thumb’ (sometimes called ‘heuristics’) for what to do, based on years of experience, has been shown in some studies to be an effective way of treating patients. 6 This becomes more common when the subject you are trying to create guidelines for gets more specialised and there are less research papers available on the subject.

Another issue is that guidelines are made to apply to an entire population. Thus, when you are trying to treat an individual patient in front of you, sometimes the broad ‘one size suits all’ treatment guideline doesn’t work. For example, treatments may not work as effectively if your patient has a rare variant of the disease mentioned in the guideline. Also, what if your patient has two illnesses, and the medications recommended in one guideline would make the patient’s other condition worse? Indeed, this is becoming more common due to an ageing population, which makes the development of co-morbidities (multiple coexistent long term health conditions) more likely.

So, EBM is important because it marked a huge change in the way medicine is practiced. It has undoubtedly led to more consistent practice and better treatment for patients, but it is not without its downsides. Applying a rigid guideline to use in any scenario that doesn’t allow doctors to use their own experience brings with it drawbacks that need to be addressed in future.

In summary:

  • EBM is the practice of using the best available evidence to treat patients.
  • EBM is only a recent development.
  • A meta-analysis is a collection of similar trials that shows the overall effect of a treatment.
  • Groups like NICE review the best evidence and come up with guidelines that doctors follow to treat patients.


1 Wennberg, John, and Alan Gittelsohn. “Small area variations in health care delivery a population-based health information system can guide planning and regulatory decision-making.” Science 182.4117 (1973): 1102-1108.

2 “Hypertension | Guidance and guidelines | NICE.” 2014. 13 Sep. 2015 <https://www.nice.org.uk/guidance/cg127>

3 “Resuscitation Guidelines 2010 – Resuscitation Council (UK).” 2015. 13 Sep. 2015 <https://www.resus.org.uk/resuscitation-guidelines/>

4 Capewell, Simon, CE Morrison, and JJ McMurray. “Contribution of modern cardiovascular treatment and risk factor changes to the decline in coronary heart disease mortality in Scotland between 1975 and 1994.” Heart 81.4 (1999): 380-386.

5 Genuis, Stephen J. “The proliferation of clinical practice guidelines: professional development or medicine-by-numbers?.” The Journal of the American Board of Family Practice 18.5 (2005): 419-425.

6 Wegwarth, Odette, Wolfgang Gaissmaier, and Gerd Gigerenzer. “Smart strategies for doctors and doctors‐in‐training: heuristics in medicine.” Medical education 43.8 (2009): 721-728.

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