What is the standardized measure of the strength of the relationship between two variables when one variable is dichotomous?

• A. Biserial correlation
• B. Point-biserial correlation
• C. Pearson correlation
• D. Spearman correlation

Answer: (A)

When one variable is dichotomous (two categories) and the other is continuous, the standard way to quantify the strength of their relationship is the point-biserial correlation. This is a special case of Pearson correlation where the binary variable is coded as 0 and 1. It reflects how much the continuous variable's values differ between the two groups, standardized by the overall variability. A positive value means higher scores tend to occur in the group coded as 1, a negative value means higher scores tend to occur in the group coded as 0, and larger absolute values indicate a stronger association.

Biserial correlation, by contrast, is used when the dichotomous variable is believed to arise from an underlying continuous trait that has been split into two categories. In everyday data with an observed 0/1 dichotomy, the point-biserial approach is the appropriate and widely used measure.