When one factor changes, and another factor changes along with it, there is usually a direct relationship. Alternatively, both could be caused by a third factor; for example, two prices of unrelated goods increasing during a period of [[inflation]] (see also [[correlation is not causation]]). | When one factor changes, and another factor changes along with it, there is usually a direct relationship. Alternatively, both could be caused by a third factor; for example, two prices of unrelated goods increasing during a period of [[inflation]] (see also [[correlation is not causation]]). |