Which of the following are true about regression with one predictor variable (often called "simple regression")? Check all that apply. The regression equation is the line that best fits a set of data as determined by having the least squared error. The slope describes the amount of change in Y for a one-unit increase in X. After conducting a hypothesis test to test that the slope of the regression equation is nonzero, you can conclude that your predictor variable, X, causes Y.