Wednesday, April 25, 2012

Florence Nightingale and the rise of the pie chart

The pie chart, perhaps the only presentation tool that reminds you of dessert, is older than you think. The New York Times magazine took a look at the founder of the pie chart, William Playfair, who first used it in 1801.

Pie charts didn't catch on until the middle of the 19th century, however. Then they were used in combinations with maps to convey additional data, and expanded in shapes to include rings and "doughnut" charts. (The food imagery even carries into many languages, such as French, where a pie chart is called le camembert after the wedges of cheese it resembles.) But it took a woman presenter, famous nurse and noted statistician Florence Nightingale, to advance the pie chart in the uses for which we know it today. From the New York Times article:

Nightingale's pie charts
Florence Nightingale drove home the impact of poor sanitary conditions on mortality rates during the Crimean War by reconfiguring a pie chart, varying the length, rather than the width, of the wedges, so that the graph resembled a cock’s comb. As the historian Hugh Small notes, Nightingale may not have invented statistical graphs, but “she may have been the first to use them for persuading people of the need for change.”
You'll see few pie charts in scientific papers, as they are not considered ideal for many scientific displays. In fact, Nightingale's design improves upon the original in a way that was much later confirmed by research at AT&T Bell Laboratories, showing that comparison by angle is less accurate than comparison by length, something her design incorporates into the pie chart.

I asked readers on The Eloquent Woman on Facebook to guess which famous woman helped advance the pie chart, and Emily Dust Nimsakont was first out of the box with the correct answer. She wins a set of The Eloquent Woman's magnetic poetry. Congratulations, Emily!


Famous Women in Business said...

Two giants of graphical data analysis, William Cleveland and Edward Tufte, have little good to say about pie charts. Cleveland calls the pie chart an example of a "pop chart" for their popularity, but recommends a dot plot, for more efficient pattern perception. Tufte goes even further, saying that for the few numbers presented in most pie charts a simple text table is almost always better than "a dumb pie chart." Pie charts have to many inherent perception problems, particularly when making comparisons across an interesting explanatory variable.

Ella Kueshen said...

FW in B, That's true, but I think Mr Tufte would applaud Ms Nightingale's interest in data. It might also be worth mentioning that he gives other examples of Playfair's work. He was also, it seems, the inventor of the histogram or bar chart. It's really quite amazing to consider how recent an invention that is. I wonder too whether developing new ways of visualising data leads in turn to new metaphors or turns of phrase, and has an impact on the tools of eloquence. We might still use 'slice of the pie', but what about 'trending upwards'? No doubt you can think of more than I can.