A March 2018 Gallup survey asked a sample of 10411041 adults if they wanted stricter laws covering the sale of firearms. A total of 697697 of the survey respondents said yes. Although the samples in national polls are not SRSs, they are similar enough that our method gives approximately correct confidence intervals. How large a sample would be needed to get a margin of error half as large as the margin of error for a sample of 10411041 adults