I. In a linear regression performed on standardized (z-score) data, the slope is equal to the correlation coefficient $$r$$, and transforming back to the original units gives a slope of $$r \times \frac{s_y}{s_x}$$.

II. The slope of the regression line remains unaffected by the units of measurement for the variables.

III. Once variables are standardized, the correlation coefficient is no longer needed to compute the slope of the regression line in original units.

Which of these statements regarding regression slopes and standardization is correct?