index (i). As the number of responses is less than the number of non-responses, the responses are used to determine the 50% value. N=Sum Ni = (1+2+9+7+1+0)=20 A=Sum i*Ni=(5+8+27+14+1+0)=55 50% level = X0+d*(A/N-0.5)=3+0.45=3.45 Example 2 Testing performed at an interval of d=0.2, testing commences one step before a change in response. As the number of non-responses is less than the number of responses, the non-responses are used to determine the 50% value. N=Sum Ni = (0+2+12+1)=15 A=Sum i*Ni=(0+4+12+0)=16 50% level = X0+d*(A/N+0.5)=3.2+0.31=3.51 References J. W. Dixon and A. M. Mood (1948), "A Method for Obtaining and Analyzing Sensitivity Data," Journal of the American Statistical Association, 43, pp. 109–126. B. T. Neyer (1994), "A D-Optimality-Based Sensitivity Test," Technometrics, 36, pp. 61–70. H. A. Dror and D. M. Steinberg (2008), "Sequential Experimental Designs for Generalized Linear Models," Journal of the American Statistical Association, Volume 103, Number 481, pp. 288–298. L. D. Hampton et al, (1973), Logical Analysis of Bruceton Data, Naval Ordnance laboratory, White Oak, USA. https://apps.dtic.mil/sti/pdfs/AD0766780.pdf See also Safety Testing of Explosives Explosives engineering