Correlation versus Causation
“Cause and effect” occurs when a willful force engages in some activity with the intent to produce an effect. The caveman hurls his spear at a wooly mammoth with the intention of killing it, thereby causing its death. In R. A. Fisher's definition, cause and effect can be determined only within the framework of planned experiments. The degree to which one variable can be predicted from another can be calculated as the correlation between them. Correlation is not equivalent to cause for one major reason. Correlation is well defined in terms of a mathematical formula.