In statistics, an association (statistics) comes from two variables who are related. Many people confuse association with causation. Association DOES NOT imply causation.

For example, the United Nations did a study of government failure - when governments fall or are overthrown. The best indicator of a government about to fall was the infant mortality rate. The dead children do not cause the government to fall, rather they are joint effects of a common cause.

Another example is ice cream consumption and murder. Did you know that the sales of ice cream and murder are strongly positively correlated? Which causes which: does eating ice cream cause murder or does murder make people eat ice cream? The answer is neither -- ice cream consumption and murder are both at least partially caused by hot weather.

Several tests can be used to determine association. The P test, t-test, and chi-squared test are the most common.