What is it
Correlation measures the strength and direction of a linear relationship between two variables, quantified using the product moment correlation coefficient (a value between -1 and 1).
Why it matters
Correlation is one of the most commonly misused statistical ideas in the real world — understanding precisely what a correlation coefficient does and doesn't tell you is essential for critically evaluating data-driven claims in the news and research.
Exam tip
Never describe correlation as causation in your answer — a strong correlation coefficient only shows a linear relationship exists, not that one variable causes the other, and examiners specifically look for this distinction in written answers.
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