. | 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 | |||||||||

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. | 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 | |||||||||

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. | 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% | ||||||||

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. | 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% |

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. | 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% |