Elementary Statistics (12th Edition)

Published by Pearson
ISBN 10: 0321836960
ISBN 13: 978-0-32183-696-0

Chapter 7 - Estimates and Sample Sizes - 7-2 Estimating a Population Proportion - Beyond the Basics - Page 342: 41

Answer

p is between 0.92-0.1027=0.8173 and 0.92+0.1027=1.0227. The thing that is unusual that the upper bound exceeds 1, which is not possible for p. Modification is needed.

Work Step by Step

The best point estimate is equal to the proportion of the sample (x) divided by the sample size: $\hat{p}=\frac{x}{n}=\frac{44}{48}=0.92.$ b)$E=z_{\frac{\alpha}{2}}\cdot \sqrt{\frac{\hat{p}\cdot (1-\hat{p})}{n}}=2.575\cdot \sqrt{\frac{0.92\cdot (1-0.92)}{48}}=0.1027.$ Hence, the confidence interval: E is between $\hat{p}-E$ and $\hat{p}+E$, hence p is between 0.92-0.1027=0.8173 and 0.92+0.1027=1.0227. The thing that is unusual that the upper bound exceeds 1, which is not possible for p. Hence, modification is needed.
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