Causation is a relationship between two correlated quantities where one directly affects the other.

• Causation exists: An example of a correlation where there is also a causation is height and age. Aging directly causes growth, up until some point.

• No causation: In winter, both the number of house fires and car accidents increase — they are correlated. However, house fires do not cause car accidents. There is a potential common factor that can explain the increase in both: winter, which causes both slippery road conditions and more candles to be lit, which leads to more fires. There is a correlation, but no causation.