Nightingale was helped to understand statistics by her country's leading expert on public statistics, William Farr. He was a founder of medical statistics, and epidemiology. Farr worked with her on all the statistics from the Crimean War, which she publicised in her writing. She proved that more men had died from disease than fighting, a very important piece of information. The disease in question was mostly cholera. Cholera is caused by a bacterium spread by people drinking water contaminated by sewage. Unfortunately, both she and Farr believed the disease was caused by foul air: this was called the miasma theory.