John Snow (1813-1858)

John Snow attended school until age 14 when he became apprentice to a surgeon. He later graduated from the University of London. He became a distinguished physician and one of the first to specialize in anesthesiology. He was even asked to administer chloroform, one of the forms of anesthesia used at the time, to Queen Victoria while she was in labor. His contributions to statistics appear mostly in the creation and application of graphics for one specific scenario regarding cholera.

Cholera was originally limited to India and its neighbors except for a few farther-reaching pandemics. The first of these began in 1817, spreading to Sri Lanka and East Africa and then farther to Japan, China, and Astrakhan in Russia. There were no cures or prevention strategies at the time. A second pandemic occurred from 1826 to 1837. It spread throughout India along rivers and trade routes and made its way to Astrakhan again. This time, it spread to Moscow and from there to the Baltic States and Poland, then farther west to France and Great Britain. Then it spread across the Atlantic to Canada and New York and south and west from there. Thomas Latta, a British physician, used a saline injection to rehydrate patients, which helped to treat the disease, but leeches and laxatives were also used, and there was no data to compare the effectiveness of each treatment method. Clearly, this was before the features of well-designed experiments were developed.

Snow began working to identify how cholera was spread, looking at patterns of outbreaks from the second pandemic. He correctly suspected that the disease was spread through drinking water, but because there were many other possible causes, he needed data to convince his contemporaries. He had a breakthrough while investigating the outbreak in the Broadstreet area of London at the end of August 1853. He interviewed families of those who were sick, organizing the information in a data map, and noticed that most collected their water from the pump on Broadstreet. However, there were a few cases where the direct connection was less clear. For example, an elderly woman that had no longer lived in the Broadstreet area was infected. They later found that she preferred the taste of the Broadstreet water, so she sent for a bottle of water from the Broadstreet pump every day. Later, they discovered that the first victim in the area was a five-month old girl whose family's cesspool was only three feet from the pump. Snow's work did not look at what causes cholera, that is, whether it was a bacteria or virus or something else, but he did find a correlation between people who got sick and water source.

Snow contributed to the development of graphical analysis which is crucial to modern statistics. Before inferential methods are conducted, researchers use exploratory data analysis like looking at graphical summaries to ensure that assumptions are met and to observe anomalies. This enables researchers to get a full picture of the data and what has occurred during a study.