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In statistics, an association means there a relationship between two variables or factors.
The presence of an association or relationship does not necessarily imply causation (a causal relationship).
Observing a simple association between two variables - for example, having received a particular treatment and having experienced a particular outcome - cannot be assumed to mean that the treatment caused the outcome. The association may reflect the effects of biases from confounders.
For example, if people who choose to take a treatment have better outcomes (e.g. fewer heart attacks), the treatment is associated with the outcome. However, people who seek and receive that treatment may be healthier and have better living conditions than people who do not seek and receive the treatment, so the former have better outcomes for those reasons, rather than because of the treatment.
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