Florence Nightingale's Hockey Stick

florence-nightingale-avenging-angel.co.uk/blog/florence-nightingale-statistical-diagram/

Nightingale wanted to use the Rose Diagram to convince people that the Chief Medical Officer, John Simon, was wrong because deaths from epidemic disease were avoidable, using her evidence that deaths from sickness had been reduced during the war. So looking at the column chart which I drew in an attempt to ‘improve’ Nightingale’s chart, what is wrong with it as far as supporting Nightingale’s sanitarian message? It has 3 defects:

The war lasted exactly two years, and fortuitously the Sanitary Commission and the death rate reduction arrived exactly in the middle; she wanted to compare the two years to show the situation ‘before and after’, but the column chart simply contrasts each month with preceding and succeeding months. Obviously the answer was to split the two years in some way;

As well as obscuring the comparison of years, it obscures the comparison of seasons. You have to hunt for the month letters on the horizontal axis. The answer here would be to line up the years with each other after you’ve split them.

The staggeringly high mortality in the first January (decimation of the army in a single month) gives the impression that ‘General Winter’ was to blame, or at least distracts the viewer from the intended ‘before and after’ message. Her answer to this was downplay month on month variation by doing a square root transformation, using areas.