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Unformatted text preview: a certain trait or opinion ( p ). Newspapers and magazines routinely survey only one or two thousand people to determine public opinion on current topics of interest. ˆ When a survey is used to find a proportion based on a sample ( p ) of only a few thousand individuals, one question is how close that proportion comes to the truth for the entire population. This measure of accuracy in sample surveys is a number called the margin of error. ˆ The margin of error provides an upper limit on the amount by which the sample proportion p is expected to differ from the true population proportion p , and this upper limit holds for at least 95% of all random samples. To express results in terms of percents instead of proportions, simply multiply everything by 100. Conservative (approximate 95%) Margin of Error = 1 n where n is the sample size. We will see where this formula for the conservative margin of error comes from in Chapter 10 when we discuss in more detail confidence intervals for a population proportion. For now we will consider an approximate 95% confidence interval for a population proportion to be given by: Approximate 95% Confidence Interval for p:...
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