Calculates the slope and intercept of the regression line. This function
differs from linear-regression-minimal' in that it takes summary statistics:<br> x' and y' are the sums of the independent variable and dependent variables,<br> respectively; x2' and y2' are the sums of the squares of the independent<br> variable and dependent variables, respectively; and xy' is the sum of the
products of the independent and dependent variables.
You should first look at your data with a scatter plot to see if a linear model
is plausible. See the manual for a fuller explanation of linear regression
statistics.