Figure 2. In this hypothetical example, the median effective concentration appears to be better estimated by taking the more frequent outcome, effective tests. Calculation template: Average of tests +/- the half testing interval = EC⁵⁰. Ineffective tests: (0 x 4)/4 + (0.01)/2 = 0.005% wt/vol. Effective tests: [(0.01 x 4) + (0 x 6)]/10 - (0.01)/2 = -0.001% wt/vol.