Estimation of the Mean and Proportion John （约翰估计均值和比例）.pdfVIP

CHAPTER 8 Estimation of the Mean and Proportion CHAPTER OUTLINE 8.1 Interval Estimation of a Population Mean: 8.4 Determining the Sample Size for the Large Samples or σknown Estimation of Mean 8.2 Interval Estimation of a Population Mean: 8.5 Determining the Sample Size for the Small Samples or σunknown Estimation of Proportion 8.3 Interval Estimation of a Population Proportion: Large Samples 8.1 INTERVAL ESTIMATION OF A POPULATION MEAN: LARGE SAMPLES OR σ KNOWN When the sample size is large (n ≥30), the margin of error of estimate for a confidence interval for µ can be found with Excel’s CONFIDENCE function. This function has three inputs: 1) the confidence level subtracted from 100%, entered as a decimal, α = Alpha 2) the standard deviation of the population, σ = Standard_dev (use s, the sample standard deviation, if σ is not known) 3) the sample size, n = Size. 107 108 Chapter 8 Estimation of the Mean and Proportion This margin of error of estimate can then be subtracted from and added to the sample mean in order to construct the interval. Indeed, recall that the endpoints of such a confidence interval are as follows: σ x ±z σ , where σ . x x n Here, n is the sample size, σis the population standard deviation, and z is the cut-off for confidence level = α. If n is large and σis not known, then it can be replaced by s, the sample standard deviation. Example 8-1 A publishing company has just published a new college textbook.