Chapter 10 Confidence interval estimation part 2.docx
10.3 Confidence interval estimation for the proportion
• Estimating the proportion of items in a population having a certain characteristics
• The unknown population proportion is represented by π. The point estimate for π
is the sample proportion p=X/n, where n is the sample size and X is the number
of items in the sample having the characteristics of interest.
• You can use the confidence interval estimate of the proportion defined in
equation to estimate the proportion of sales invoices that contains errors.
• Equation contains a Z statistic because you can use the normal distribution to
approximate the binomial distribution when the sample size is sufficiently large. 10.4 Determining sample size
Sample size determination of the mean:
• To compute the sample size, you must know three factors:
1) The desired confidence level, which determines the value of Z, the critical
value from the standardize normal distribution
2) The acceptable sampling error
3) The standard deviatio