Causal Model

1. Viruses and bacteria in wounds cause infection and death.
2. Viruses and bacteria are carried around by dirty hands.
3. Hence dirty hand cause death.
4. Viruses and bacteria can (largely) be washed off.
5. Clean hands carry fewer viruses and bacteria around than dirty hands.
6. Therefore we wash hands to avoid infection and death.

Correlation

1. Some wards have few hand washes and many deaths.
2. Some wards have many hand washes and few deaths.
3. Wards with both few hand washes and few deaths are very rare.
4. We infer that there is a decreasing function $y=f(x)$ giving the approximate number of deaths $y$ as a function of the number of hand washes $x$.
5. Therefore we wash hands to avoid infection and death.

Machine Learning