The r.m.s. error of the regression line is the root-mean-square of the resid-

uals. This measures the accuracy of the regression predictions. The predictions are off by amounts similar in size to the r.m.s. error. For many scatter diagrams, about 68% of the predictions will be right to within one r.m.s. error. About 95% will be right to within two r.m.s. errors. pl875