Ockham's razor

Douglas Wardrop (JRSM 2008;101:50–1) is right in commenting that the scholastic logic of Ockham's razor is of limited relevance to geriatric medicine. Geriatricians have long taught their students that if an old person admitted to hospital has less than 5.5 or 6.5 diagnoses he or she (respectively) may have been inadequately assessed. But I was surprised to see so little deference to probability in the Editorial. It is not the number of different ‘entities’ – a fine scholastic concept – but their probabilities that matters. One of my patients with ulcerative colitis developed a peripheral arthropathy that the literature claimed as a rare complication of chronic bowel disease. Calculation revealed that it was much more likely that she had rheumatoid arthritis as well as her bowel disease rather than the single diagnosis decreed by Ockhamism. Conversely, decades before Lewy Body Disease was defined it was obvious that Parkinsonism (clinically diagnosed) and dementia (also clinically diagnosed) occurred together far more often than was compatible with independent incidence. This prophesied the existence of at least one unrecognised unifying ‘entity’. But probabilities varying with sex, age and other demographic factors can be difficult to estimate from conventional medical literature. How much easier both clinical diagnosis and research would be if the NHS had an accessible system of epidemiologically structured medical records matching that of an American Health Maintenance Organization. We could then forget the scholastics.

Footnotes

Competing interests None