This demonstration allows you to specify a prediction line and see how well it fits the data. When the simulation begins, the prediction line is a horizontal line that goes through the mean of Y. The equation for the line is shown at the bottom of the graph. Since the line is horizontal, it has a slope of 0. The intercept is the mean of Y. The SSE and MSE are also shown. The SSE is the sum of squares error which is equal to the sum of the squared deviations of the points from the line. The MSE is the SSE divided by N-2 where N is the number of points. The SSE and MSE indicate how well the line fits the data. If the fit were perfect, they would both be 0. The point of this demonstration is to allow you to change the prediction line and see its effects on the SSE and MSE.

To change the intercept of the line, click and hold somewhere in the middle of the line and move the line up or down. As you move the line, you will see that the intercept as well as the SSE and MSE change.

To change the slope, click and hold the line at the left end of the line and drag the line down or up. Or, you can click and hold the right end of the line and drag up and down. Notice that as the slope changes, the SSE and MSE change as well.

To see the best-fitting line, click the "Show regression line" button. The best-fitting line is shown in red, as are the SSE and MSE.