Everyone knows the lamp; few know she was a brilliant STATISTICIAN. In the Crimea she saw soldiers dying not of wounds but of preventable disease — filth, not bullets — and to make the generals SEE it she invented a diagram: a rose where each month is a wedge whose AREA is the death toll, disease in one colour dwarfing battle in another. Slide the months and read the war.
Nightingale’s coxcomb (polar-area) diagram encodes each month’s mortality as a wedge whose AREA — not radius — is proportional to the deaths, so the eye reads magnitude honestly (radius ∝ √value, since a wedge’s area ∝ r²). Her data showed deaths from ‘zymotic’ (preventable) disease overwhelming deaths from wounds. A fail-loud self-check throws unless the radius-as-√value rule makes wedge area exactly proportional to the death count, and the disease toll exceeds the wound toll — the argument that won sanitary reform.
Representative figures in the spirit of her 1858 Crimean data (disease vastly exceeded battle deaths); the exact monthly counts varied. The area-proportional encoding and the disease>wounds relation are exact as shown.