How razor blades can make you better at diagnosis

Pluralitas non est ponenda sine necessitate – that’s right… this study hacks an old one.

“Plurality should not be posited without necessity…”

No? How about…

The simplest entity is the one to be the preferred

Still not getting it?… how about…

“Don’t over complicate it”

Now I don’t know about you, but nothing quite gets me going like scholastic philosophers of the 13th century. Combine such philosophers with a means to be a better diagnostician and its no wonder that I’d cross William of Ockham at some point.

Who is he? What’s he got to do with razors and how is this going to make your diagnostic skills sharper… let me reveal all.

🥜Article in a nutshell

  • What is the Occam’s razor?
  • Why medical students need to know about it
  • How to use Occam’s razor to perform better in MCQs and OSCEs
  • A note on the contrary

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🤔What is Occam’s razor?

In the late 13th century, William of Ockham, a Franciscan friar and philosopher posited that “plurality should not be posited without necessity.”

What he was really saying is that the simplest explanation is usually the correct one.

Applied to medicine, this can mean that when you are trying to diagnose a patient, the simplest explanation is often the right one.

Ockham’s razor is also known as the law of economy or the principle of parsimony. It is a problem-solving principle that states that when you have two competing theories that explain the same thing, the simpler theory is usually better. He was sharp with his enforcement of this belief, so sharp it was locked in history as Occam’s (or Ockham’s) Razor.

✌️Why all medical students need to know about Occam’s razor

Occam’s razor can help you score higher on both your paper and practical exams.

When applied to MedEd, the principles implies that when you see a range of signs and symptoms together, you should always* attempt to attribute them to a single disease process, rather than many different diseases.

Occams razor helps with MedEd when it comes to:

  • Diagnosing patients in osces/paces who may have multiple signs
  • In written papers, where the vignette (question) may describe a range of signs and symptoms before asking for the most appropriate diagnosis, intervention or management plan.

In both cases, you’ll need to ask yourself ‘how do all the signs and symptoms relate together?’

*Occam would say always, take a look at the last section before you come at me.

🖐️An Example of Occam’s razor in action.

Let’s say you found yourself in an OSCE/practical exam with a gentleman with a murmur.

He’s in his 60s, overweight, has a relatively young sternotomy and saphenous vein graft scar, tar-stained fingers, and a pan systolic murmur heard loudest in the 5th intercostal space mid-clavicular line, and loudest on rolling to the left-hand side during expiration. What’s causing the murmur?

There are lots of causes of murmurs, but think of Occam’s razor – how can you slash away until you get a unifying cause? William of Ockham would tell you that that’s the most likely cause.

Well, combining his tar stained fingers and BMI, he has cardiovascular disease risk factors. A young sternotomy scar and saphenous vein graft points towards recent CABG surgery (in keeping with cardiovascular risk factors). The murmur has characteristics that makes it loudest in the mitral region.

Combining this all together you could deduce that his murmur has arisen from a recent MI. An acute myocardial infarction can cause chordate tendinae rupture, causing mitral regurgitation and therefore a murmur in keeping with this presentation. Thanks William of Ockham.

⚠️Occam’s razor doesn’t always work though

A polar opposite view of this decision-making hack is that of John Hickam. Doctor Hickam was an American physician who was Chair of the Department of Medicine at the University of Indiana. Hickams Dictum challenges Occam’s razor

“patients can have as many conditions as they damn well please”

We see patients on a daily basis who come in with one problem but then develop another condition on top. this could include a UTI, chest infection, delirium or cellulitis to name a few. Hickam’s Dictum is a reminder that medicine is never clear cut and we should always consider that the unifying diagnosis, although plausible, may not be the only reason.


Overall the message here is that when faced with multiple signs and symptoms, in the first instance, try and slash away to find a unifying diagnosis.

Can you link as many signs as possible in the question of a multiple choice question to pin down a diagnosis?

In practical exams, picking up as many signs as possible will help you to whittle down to one (or few) unifying cause(s). Occam’s razor would say to trust the simplest explanation for all signs together, as the underlying cause.

To quickly summarise everything we’ve covered today:

  • What is occams razor? A problem-solving principle that states that when you have two competing theories that explain the same thing, the simpler theory is usually better
  • Why should medical students know it? It can help you score higher on both your paper and practical exams.
  • How Occam’s razor can help you become better at diagnosis? By applying Occam’s razor to your problem solving, you can quickly arrive at the most likely diagnosis by eliminating competing differentials.
  • A note on the contrary – Hickam’s dictum states that “patients can have as many conditions as they damn well please” and challenges the view that Occam’s razor.

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I hope this helps!

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