r
Correlation Coefficient Calculator
Pearson's r: how closely two sets of paired numbers follow a straight line.
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How it's calculated
r = Σ(x − x̄)(y − ȳ) ÷ √( Σ(x − x̄)² × Σ(y − ȳ)² )
r runs from −1 (a perfect falling line) through 0 (no straight-line relationship) to +1 (a perfect rising line). It measures linear association only, it is pulled by outliers, and correlation alone does not show that one thing causes the other. The p-value tests r against zero (t with n − 2 degrees of freedom).
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