What does Pearson's r indicate?

• A. The probability of rejecting the null.
• B. The mean difference between two groups.
• C. The proportion of variance explained by a factor.
• D. The strength and direction of a linear relationship between two continuous variables.

Answer: (D)

Pearson's r measures the strength and direction of a linear relationship between two continuous variables. The sign shows whether they move together (positive) or in opposite directions (negative), while the magnitude indicates how tightly the data points cluster around a straight line, with values near ±1 signaling a strong linear relationship and values near 0 signaling little linear association. It assumes the relationship is roughly linear and that the data are on interval or ratio scales, and it can be sensitive to outliers. It does not convey causation, nor does it describe mean differences or the proportion of variance explained (that latter idea is captured by r squared in regression).