Which one of the following statements is incorrect?

a. The scattergraph method can be somewhat subjective depending on where one visually places the regression line.

b. The scattergraph method is the most accurate method of analyzing mixed costs.

c. When graphing mixed costs, the dollars go on the vertical axis, and the level of activity goes on the horizontal axis.

d. Regression lines attempt to minimize the average distance between all the data points and the fitted regression line.

e. The slope of the regression line is equal to the variable cost per unit of activity.