A relationship between two variables, such that the value of one variable can be used to generate an expectation about the value of the other. A correlation may occur because one variable is causally related to the other (e.g., cell phone use while driving may be correlated with auto accidents because speaking on the cell phone directly contributes to accidents) — but correlations may also occur for other reasons. For example, it’s possible that cell phone use and accident rates are correlated because people who are prone to getting in car accidents are more likely to spend a lot of time on cell phones. It’s important to remember that a correlation between two variables does not necessarily mean that one causes the other.
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