Winfried Steiner Christiane Belitz Stefan Lang Semiparametric Stepwise Regression to Estimate Sales Promotion Effects. 590-597 2005 GfKl http://dx.doi.org/10.1007/3-540-31314-1_72 conf/gfkl/2005 db/conf/gfkl/gfkl2005.html#SteinerBL05