. richardcharnin.com . . http://www.electionmathematics.org/em-exitpolls/Exit_Polls_2004_Edison-Mitofsky.pdf . Margin of Error and corresponding Win Probability over a range of respondents and vote shares . . N= poll sample respondents . S= winning 2-party poll share . C= Cluster effect (exit poll only, zero for pre-election polls) . Formulas: . MoE = (1+C) * .98 / sqrt (N) is a good approximation when S is 50-60% . MoE = Margin of error = (1+C) * 1.96 * sqrt (S* (1-S) / N) is a more general formula used below. . Win Probability = NORMDIST(S, .5, MoE/1.96, true) . . The confidence level (probability) is 95% that the True Vote will fall within the range: S - MoE < S < S + MoE . . Sample Input: 2-party . N - respondents 13660 13660 52.38% National Exit . S - EP win share 52.4% 52.4% 51.78% State Aggregate . C- cluster effect 30% 30% . . Calculations: . Margin of Error 1.09% . Win Probability 100.00% . . . 2-party Winning Poll Share (S) . 51.8% 52.4% 53% 54% 62% 70% 80% 90% . 2004 NEP 2004 Ohio 2008 NEP . . Margin of Error . N-Sample . 500 5.69% 5.69% 5.69% 5.68% 5.53% 5.22% 4.56% 3.42% . 1000 4.03% 4.02% 4.02% 4.02% 3.91% 3.69% 3.22% 2.42% . 1500 3.29% 3.29% 3.28% 3.28% 3.19% 3.01% 2.63% 1.97% . 2004 Ohio 2020 2.83% 2.83% 2.83% 2.83% 2.75% 2.60% 2.27% 1.70% . 3000 2.32% 2.32% 2.32% 2.32% 2.26% 2.13% 1.86% 1.40% . 10000 1.27% 1.27% 1.27% 1.27% 1.24% 1.17% 1.02% 0.76% . 2004 NEP 13660 1.09% 1.09% 1.09% 1.09% 1.06% 1.00% 0.87% 0.65% . 2008 NEP 17836 0.95% 0.95% 0.95% 0.95% 0.93% 0.87% 0.76% 0.57% . . Win Probability . . 500 73.22% 79.58% 84.94% 91.63% 100.00% 100% 100% 100% . 1000 80.96% 87.88% 92.81% 97.45% 100% 100% 100% 100% . 1500 85.84% 92.39% 96.33% 99.16% 100% 100% 100% 100% . 2004 Ohio 2020 89.35% 95.17% 98.11% 99.72% 100% 100% 100% 100% . 3000 93.55% 97.86% 99.43% 99.96% 100% 100% 100% 100% . 10000 99.72% 99.99% 100.00% 100% 100% 100% 100% 100% . 2004 NEP 13660 99.94% 100.00% 100.00% 100% 100% 100% 100% 100% . 2008 NEP 17836 99.99% 100.00% 100% 100% 100% 100% 100% 100%