The Gold Standard of Patient-Centred Evidence-Based Medicine
Good science measures the outcome of an intervention on a subject and a control. The less identical the subject and control, the less reliable will be the outcome.
An engineer can compare outcomes on identical subjects, which is why your mechanic can give you a money-back guarantee. A doctor doesn’t have 10 copies of any patient (except in twin studies or in the lab) so the conclusions of his science are much less reliable.
When patients are involved, controls are created by randomisation. You take a population and randomise that population into one or more groups.
While this might create two similar groups, they are by no means identical. Nor are any two patients within any of the groups identical. The hope is that any variables that could influence the outcome are distributed evenly between the groups. While you can use design or statistics to control for factors which might influence the outcome, there are many unknowns that cannot be controlled for. Genetics, past trauma, adverse childhood experiences, diet and many others add to the noise which might contaminate the observed outcomes.
Medicine tries to compensate for that noise with numbers, but numbers just add to the noise. The bigger the group, the less likely any intervention will be applicable to any individual.
Population based results become less applicable to the individual in the same way that individual results may not be relevant to the group.
If we want to get closer to the truth, we have to pay attention to the quality of the control.
If the control and the treatment subject are identical in all respects, then a reliable result can be achieved. If we want to run a trial of a treatment 20 times to reduce the effects of chance, would it be better to do the experiment on 20 different people or run the same intervention twenty times on the same subject?
If a patient can act as their own control, then we achieve the gold standard of evidence for that patient, and it is within the control of the clinician.
To demonstrate this principle, let me show you this patient who had a headache for 27 years and watch as we use the patient as their own control and we can do this as many times as we need to, to be sure that the treatment we are proposing will have the desired effect – which it did. Her headache vanished and never returned when the tooth problem was sorted.
Eventually it becomes a pattern. Of course, we cannot make any assumptions about groups generally, but in these cases, if removing the offending foreign body results in complete resolution of symptoms then we have proven causation in these cases. To be absolutely sure, we would have to reinstate the offending crown, so far none of my patients has wanted to pay for that, and there may be a few ethical issues with that line of enquiry.
This is true patient-centred evidence-based medicine. Patient-centred must mean more than the patient agreeing to the treatment. It must mean that the treatment is tailored to the patient, and this can only be achieved by using the patient as their own control.