Comparison of two regression lines over a finite interval.

The likelihood ratio test is presented for testing the equality of two regression lines versus the ordered alternative that Line 1 lies above Line 2 on a prescribed finite interval of values of the independent variable. Homoscedastic normal errors are assumed. An application is discussed and data from it are used to illustrate the methodology. A table of exact critical values is presented for alpha = .01, .05 and .10 for various degrees of freedom. Power comparisons are made with competing tests.