PartReg :   segmented linear regression with breakpoint and extended horizontal trend at the start or the end.
Totally free download of software


The PartReg computer program (model) is designed to perform a partial segmented linear regression of one dependent variable (Y, e.g. plant growth, crop yield) on one (X) independent (explanatory) variable (predictor), e.g. crop growth factors like depth of water table and soil salinity with the aim to find the water table and salt tolerance level, also called the "no effect" range.


The segmentation is done by introducing a breakpoint and finding the stretch (at the beginning or at the end of the X-domain over which the Y-X relation can be considered horizontal, i.e. Y is not influenced by X. The regression coefficient (i.e. the slope of the line over the selected stretch) may not be significantly different from zero in statistical sense.
      Two types of functions (3 and 4) are used. In Type 3 the horizontal line is followed by a sloping line whereas in type 4 the sloping line is followed by a horizontal line.
      The horizontal line is found by partial regression over the head end (Type 3) or the tail end (Type 4) of the X domain.

Difference with SegReg:

The PartReg program is similar to SegReg. However, SegReg minimizes the deviations of the calculated values from the observed values over the entire domain and comes with a broken line fitting all data as well as possible. PartReg, on the other hand considers only that part of the domain over which the relation is horizontal. As a result the stretch over which the line is horizontal is usually longer than with SegReg, but the fit of the data in the sloping segment is not so good.
          An illustration of the difference follows. For more examples see this article on page 13 and following.


The salt tolerance (or response) of field crops under farming conditions in irrigated lands is analyzed in tolerance paper for cases in Egypt, India, and Pakistan.


Go to:

& models

General articles
& manuals

(in Spanish,
en Español)

reports & cases

reports & cases

& answers


Explanation of the difference between SegReg and PartReg

Example SegReg response Type 3 :
wheat yield
              and soil salinity
The salt tolerance of wheat in this example of Type 3 is about 5 dS/m

Example PartReg response Type 3 with extended
horizontal line using the same data as above
partial regression wheat and salt
The crop tolerates a soil salinity up to about ECe=7.1 dS/m,
which is higher than in the figure above
Example SegReg response Type 4:
yield and depth
The crop does not tolerate a depth of the water table less than 7 dm.

Example PartReg response Type 4 with extended
horizontal line using the same data as above
partial regression of
              crop yield and water level
The crop prefers a watertable deeper than 5 dm, so it tolerates
a shallower watertable than in the above figure.