Answer: The variation of the dependent variable.

The total sum of squares (SST) in simple linear regression analysis measures the variation of the dependent variable (Y). Option A is incorrect because a scatter plot represents the relationship between two variables in two dimensions, not the variation of Y. Option C is incorrect because SST specifically quantifies the variation of the dependent variable, not paired observations between variables. This concept is fundamental in understanding how the least squares criterion estimates regression coefficients and their interpretation.

Author: LeetQuiz Editorial Team