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Tag: Precision

The Quantified Doctor

flying cadeucii88.2 % of all statistics are made up on the spot
– Victor Reeves

There’s a growing movement in medicine in general and imaging in particular which wishes to attach a number to everything.

It no longer suffices to say: “you’re at moderate risk for pulmonary embolism (PE).”

We must quantify our qualification.

Either by an interval. “Your chances of PE are between 15 and 45 %.”

Or, preferably, a point estimate. “You have a 15 % chance of PE.”

If we can throw a decimal point, even better. “You have a 15.2 % chance of PE.”

The rationale is that numbers empower patients to make a more informed choice, optimizing patient-centered medicine and improving outcomes.

Sounds reasonable enough. Although I find it difficult to believe that patients will have this conversation with their physicians.

“Thank god doctor my risk of PE is 15.1 % not 15.2 %. Otherwise I’d be in real trouble.”

What’s the allure of precision? Let’s understand certain terms: risk and uncertainty; prediction and prophesy.

By certainty I mean one hundred percent certainty. Opposite of certainty is uncertainty. Frank Knight, the economist, divided uncertainty to Knightian risk and Knightian uncertainty (1).

What’s Knightian risk?

If you toss a double-headed coin you’re certain of heads. If you toss a coin with head on one and tail on the other side, chance of a head is 50 %, assuming it’s a fair coin toss. Although you don’t know for certain that the toss will yield head or tail, you do know for certain that the chance of a head is 50 %. This can be verified by multiple tosses.

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