Field data on crop susceptibility factors (CS) and stress-day factors (SEW30) were reviewed and evaluated. The effects of CS factors and their corresponding values of normalized crop susceptibility factors (NCS) on the relationship between stress day index (SDI) and relative yield (RY) were evaluated. Different sets of CS and NCS values for corn, obtained from different locations in the world, were also compared. The results of this study indicate that the relationships developed between SDI and RY by using CS factors will be significantly different from the ones developed by using the corresponding NCS factors. Also, the use of CS values from other locations could be acceptable for calculating the SDI values for drainage design if local data on SEW30 factors are available.