Inc. All Rights Reserved. It is expressed in the square of the units used for the Y values. The value s y.x is the standard deviation of the vertical distances of the points from the line. The value R 2 quantifies goodness of fit. It is a fraction between 0.0 and 1.0, and has no units.
Higher values indicate that the model fits the data better.
You can interpret R 2 from nonlinear regression very much like you interpret r 2 from linear regression. A high R 2 tells you that the curve came very close to the points. When R 2 equals 0.0, the best-fit curve fits the data no better than a horizontal line going through the mean of all Y values. If you know X you can calculate Y exactly. R 2 is computed from the sum of the squares of the distances of the points from the best-fit curve determined by nonlinear regression.