How to understand medical decisions

Evidence based medicine

‘Evidence-based medicine’ refers to the use of medical treatments and other procedures such as tests which have been demonstrated to work by using carefully chosen conventions based on studies on groups of patients.  However, a transparent self-explanatory summary contains all the treatments taken by an individual patient, together with the diagnoses and supportive findings, whether a carefully conducted study has shown that they ‘work’ or not.  Treatments that ‘work’ are regarded as those that provide extra benefits over and above the placebo effect.  If patients believe that a treatment works (even if it does not) then this may make them feel better; this is called the ‘placebo’ effect.  


There are two reasons why treatments that do not work should be included in a transparent self-explanatory summary.  (1) Some ineffective ‘treatments’ can cause harm when they are taken in combination with other effective treatments.  For example, some ineffective herbal remedies that produce placebo effects may contain substances that can interfere with the ability of other treatment (e.g. blood thinning medication) to do its work. (2) Some ineffective treatments may be given for lethal or other serious conditions which could be treated effectively using treatments based on factual evidence.  A trained doctor will be able to spot these if they are recorded in a self explanatory summary.


Evidence based medicine (EBM) as currently taught does not cover all aspects of medical practice however.  It focuses on evidence for the effectiveness of treatment (where it emphasises the role of randomised controlled trials) and the effectiveness of adjusting the cut-off points for population screening tests (by applying the indices of sensitivity, specificity,the likelihood ratio, and a 'receiver-operator characteristics' plot of the latter).  Books and articles on EBM do not in general:


1. specify the actual symptoms, examination findings and test results experienced by an individual patient that were used to choose each treatment so that they can be compared carefully to the findings of groups of patients described in publications.  


2. refer to studies that provide the proportion of patients who have each diagnosis in a list that cause symptoms, examination findings or test results.  


3. refer to the frequency of occurrence of findings in one diagnosis compared to another in order to distinguish between them when they occur in a list of causes.  


4. explain how diagnostic and treatment criteria can be chosen so that they maximise benefit to patients when they are treated for these diagnoses and treatment criteria.  


These topics are explained in the Oxford Handbook of Clinical Diagnosis however.



© Huw Llewelyn 2016