While working in Scutari in 1854 during the Crimean War, Florence Nightingale suspected that only some soldiers' deaths were attributable to their wounds. Instead, she thought they were mostly dying because they were malnourished, over-worked and ill-clothed. At that time, people were not aware about how diseases were transmitted but Nightingale started to record all admissions, deaths and causes of deaths. In doing so, she was able to detect a pattern and form associations. She found that the majority of deaths were due to what she called 'preventable' or 'mitigable zymotic diseases', what we today call 'infections'.
She then obtained William Farris's mortality tables from the General Registry Office. These tables listed causes of death in general population and Nightingale compared his numbers with her own data on the mortality of soldiers. She did this to great effect. She proved that a soldier - even in peacetime - had twice the risk of dying in a given year than a civilian. she then showed that in periods of heavy fighting, far more soldiers died from infection than from wounds sustained in a battle.
Armed with this information (and beautifully illustrated in her plotted statistics), Nightingale championed for better conditions in the barracks. She was successful in setting up a Royal Commission of Inquiry into the sanitary conditions during the Crimean War. Health and housing was also a big issue for Nightingale but unfortunately, her attempts to get questions on these subjects added to the census fell on deaf ears.
Nightingale was a public health practitioner. She identified a health need, compiled the evidence and used it to make policy and to take action. The outcome was a better lot for soldiers for centuries.