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American Scientist, by Howard Wainer, Shaun Lysen
The most exciting phrase to hear in science, the one that heralds new discoveries, is not "Eureka" but "That's funny..."
Isaac Asimov (1920-1992)
The Princeton polymath John Tukey (1915-2000) observed that "the greatest value of a picture is when it forces us to notice what we never expected to see." A graphic display can only develop the sort of forceful personality Tukey suggested when it is prepared carefully. As we shall see, when the combination of interesting data and clever display are properly aligned, remarkable outcomes can result.
Historically bacteria have been classified by a variety of characteristics—their physical features when viewed through a microscope, their response to various stains, their interactions with chemical agents and so on. In the mid- 20th century a new set of criteria began to be added—how they are affected by specific antibiotics.
In 1951, the famous graphic designer Will Burtin (1908-1972) published a graphic display that was admired for the clarity and economy with which it showed the efficacy of three antibiotics on 16 different kinds of bacteria. The dependent variable was the minimum concentration of the drug required to prevent the growth of the bacteria in vitro—the minimum inhibitory concentration (MIC). The three drugs were penicillin, neomycin and streptomycin, and their efficacy varied over six orders of magnitude. The original data and the representation of the data devised by Burtin are shown on the facing page (top). The scale varies from 1,000 micrograms per milliliter on the innermost ring to .001 micrograms per milliliter on the outermost; the longer the bar, the greater the efficacy of the antibiotic.
The clustering of bacterial types and sensitivity to antibiotics becomes even more evident with a simple scatterplot in which we plot each bacteria's MIC for both neomycin and penicillin. Streptomycin, not shown, has MIC values similar to neomycin. The penicillin response is quite different from the other two.
But these more specific plots were only generated after we knew what to look for—after the display shown at left allowed us to see what we hadn't expected.
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