What is a statistical measure indicating the extent of the relationship between two variables called?

The statistical measure indicating the extent of the relationship between two variables is known as the correlation coefficient. This coefficient quantifies the degree to which two variables are related, showing both the strength and the direction of the relationship. A correlation coefficient can range from -1 to 1; a value close to 1 indicates a strong positive relationship, while a value close to -1 indicates a strong negative relationship. A value of 0 suggests no relationship between the variables.

The other options represent different statistical concepts. The regression coefficient relates to the slope of the regression line in a regression analysis, indicating how much one variable changes in response to a change in another variable, rather than measuring the relationship's strength directly. Standard deviation is a measure of the amount of variation or dispersion in a set of values, and variance is the square of the standard deviation, representing the average of the squared differences from the mean. These concepts do not specifically gauge the extent of the relationship between two variables as the correlation coefficient does.