This is not the same as minimizing the sum of squares of the distances (as seen on the graph) between points and curve. The nonlinear regression analysis minimizes the sum of the squares of the difference between the actual Y value and the Y value predicted by the curve. Yintercept is the Y value when log(X) equals 0.0. Slope is the change in log(Y) when the log(X) changes by 1.0. But when you fit the data, the two fits will not be quite identical. Since both axes are transformed the same way, the graph is linear on both sets of axes. Equations Semilog line - X axis is logarithmic, Y axis is linear Click Analyze, choose Nonlinear regression (not Linear regression) and then choose one of the semi-log or log-log equations from the "Lines" section of equations. Change one or both axes to a logarithmic scale.ģ. Go to the graph, double click on an axis to bring up the Format Axis dialog.
Create an XY table, and enter your X and Y values.Ģ. In contrast, nonlinear regression to an appropriate nonlinear model will create a curve that appears straight on these axes. In these cases, linear regression will fit a straight line to the data but the graph will appear curved since an axis (or both axes) are not linear. Prism's collection of "Lines" equations includes those that let you fit nonlinear models to graphs that appear linear when the X axis is logarithmic, the Y axis is logarithmic, or both axes are logarithmic. Since Prism lets you choose logarithmic axes, some graphs with data points that form a straight line follow nonlinear relationships. The nonlinear regression analysis fits the data, not the graph. Straight lines on graphs with logarithmic axes
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