When you select Piecewise linear regression from the Nonlinear Estimation Startup Panel - Quick tab, STATISTICA estimates, using least squares, the model:

y = (b01 +b11 *x1 +...+bm1 *xm )*(y ≤ bn ) + (b02 +b12 *x1 +...+bm2 *xm )*(y > bn )

Thus, STATISTICA estimates two separate linear regression equations; one for the y values that are less than or equal to the breakpoint (b0) and one for the y values that are greater than the breakpoint. (For a general description of these types of models, see Common Nonlinear Regression Models.)

To estimate models with breakpoints (discontinuities) in the independent variables, choose User-specified regression from the Nonlinear Estimation Startup Panel - Quick tab, and then use logical operators in the model equation to define the breakpoints.