UNCERTAINTY
Uncertainty in Medicine and Public Health Professor Sir Christopher Whitty (Pembroke College, 1985) Chief Medical Officer (CMO) for England, the UK government’s Chief Medical Adviser and head of the public health profession
‘Medicine is a science of uncertainty and an art of probability’ is one of the better-known aphorisms of Sir William Osler. I have been asked to reflect on the first of these: how we handle uncertainty in medicine and public health. Osler, who died during the great influenza pandemic of 1918-19, did not have access to the range of radiology, diagnostic instruments, blood tests, microbiological data and statistical techniques that we do today. These help us to reduce uncertainty to a greater degree, or to do so more quickly, than doctors in Osler’s time - but uncertainty often remains before we have to act. Management of patients and public health in the face of uncertainty therefore remains central to medical practice, and always will. There are some important differences between clinical practice and public health practice in how, as a profession, we make decisions whilst there is still uncertainty. Every discipline within medicine operates with different levels of uncertainty and handles it slightly differently. There are however some common themes for all of us. Every Oxford medical graduate reading this will have a better understanding of how they handle uncertainty in their own discipline than I would, but common to all of them are some important trade-offs that we are often not explicit about to the public, our patients and sometimes ourselves. My own biases in handling uncertainty are framed by a career in infectious diseases, acute medicine, epidemiology and public health. An experienced surgeon or general practitioner would have a different framework but with many common themes. The first is the trade-off between speed and certainty. Whether dealing with a patient who first presents in A&E or general practice, or a new public health emergency, we start with substantial uncertainty and aim to reduce it as quickly as possible. In clinical medicine this is through history, examination, investigations and epidemiological data. The more time we have, the narrower the funnel of uncertainty becomes, as we systematically exclude diagnoses which initially seemed possible. For some situations, speed or decision-making has relatively little advantage and the rational response is to narrow the uncertainty to the point it is likely to be narrowed no further, even if that takes weeks or even months, and we can then give medical advice with a high degree of certainty. In other situations, including many emergency medical and surgical presentations but also public health emergencies, a delay before starting to act comes at a heavy price. Acting earlier runs the risk that the degree of uncertainty is so great we take the wrong action based on a false understanding of the problem; acting later runs the risk that precious time will be wasted and a worse outcome will ensue.
4 Oxford Medicine | Spring/Summer 2022
The second trade-off is between certainty and hazards/ benefit ratio of the treatment, whether at an individual or population level. If for a treatment the hazards and cost to the patient, wider society and the NHS are trivial, it is rational to have a low threshold for doing it, even in the face of much uncertainty about whether it is the right thing to do. For example, if one is quite uncertain whether a patient has myocardial infarction it is wholly rational to give aspirin unless there are clear contraindications; thrombolysis requires a higher degree of certainty. The more dangerous, difficult and expensive treatment is, the more we need to narrow the funnel of uncertainty by taking more time, effort and resource over diagnosis of the problem. It is important when considering this to consider wider societal costs as well as individual costs; antimicrobial resistance is an example where the risk to the individual patient of acting is usually relatively low but the risk to society of multiple prescriptions based on low probability is high. This trade-off between certainty and hazard/benefit ratio is true also at a population or public health level; an intervention such as recommending more exercise needs much lower level of certainty than something with the cost and damage to society of a full national lockdown. The third trade-off is between pragmatism and chasing a diagnosis to the end. Quite frequently in medicine we are not confident we know what the diagnosis is (considerable diagnostic uncertainty), but we are confident that all serious or life-threatening diagnoses, which are a small subset, have been reasonably excluded (low uncertainty about major harm). Alternatively, we may have narrowed it down to a small group of diagnoses which can be treated as a syndrome and accept that whilst a more definite diagnosis is possible, it is unlikely to provide much benefit to the patient. An example would be a diagnosis of pneumonia; it may be possible to find the aetiological organism but, in most hospitals, pneumonia will be treated with antibiotics to cover the great majority of likely causes. It would be possible to narrow uncertainty down further, but it would be disproportionate and probably retard final decision-making and treatment.
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….in public health emergencies, a delay before starting to act comes at a heavy price.
Crosscutting across all of these are several issues, the first of which is the strength of the science involved. In some areas of medicine, the science is sufficiently strong that an accurate aetiological diagnosis is possible with a very high degree of certainty before treatment is commenced, if we have time. The question is whether getting that level of precision is the right thing to do medically, even though it remains technically possible. In other areas, science is not yet sufficiently developed that certainty is realistic even with maximal time and resource. This can be very unsatisfactory
