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Power and Sample Size Figure 8.25: The Binomial Power and Sample Size dialog. Example Historically, 40% of the voters in a certain congressional district vote for the Democratic congressional candidate. A pollster is interested in determining the proportion of Democratic voters in an upcoming election. The pollster wants to know how sizable a difference could be detected for various sample sizes. That is, how much would the proportion of Democratic voters in the sample have to differ from the historical proportion of 40% to claim that the proportion is significantly different from the historical norm? 1. Open the Binomial Power and Sample Size dialog. 2. Select Min. Difference as the value to Compute. Enter 0.4 as the Proportion and 100, 500, 1000, 5000 as the sample sizes N1 to consider. 3. Click OK. 325
