Editing Nonlinear regression (section)

===Segmentation===
[[Image:MUSTARD.JPG|thumb|175 px|right|Yield of mustard and soil salinity]]
{{main|Segmented regression}}

The [[Independent variable|''independent'' or ''explanatory variable'']] (say X) can be split up into classes or segments and [[linear regression]] can be performed per segment. Segmented regression with [[Confidence interval|confidence analysis]] may yield the result that the [[Dependent variable|''dependent'' or ''response'' variable]] (say Y) behaves differently in the various segments.<ref>R.J.Oosterbaan, 1994, Frequency and Regression Analysis. In: H.P.Ritzema (ed.), Drainage Principles and Applications, Publ. 16, pp. 175-224, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands. {{ISBN|90-70754-33-9}} . Download as PDF : [http://www.waterlog.info/pdf/regtxt.pdf]</ref>

The figure shows that the [[soil salinity]] (X) initially exerts no influence on the [[crop yield]] (Y) of mustard, until a ''critical'' or ''threshold'' value (''breakpoint''), after which the yield is affected negatively.<ref>R.J.Oosterbaan, 2002. Drainage research in farmers' fields: analysis of data. Part of project “Liquid Gold” of the
International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands. Download as PDF : [http://www.waterlog.info/pdf/analysis.pdf]. The figure was made with the [[SegReg]] program, which can be downloaded freely from [http://www.waterlog.info/segreg.htm]</ref>