Statistics: Informed Decisions Using Data (4th Edition)

Published by Pearson
ISBN 10: 0321757270
ISBN 13: 978-0-32175-727-2

Chapter 9 - Section 9.1 - Assess Your Understanding - Explaining the Concepts - Page 439: 48

Answer

1060 is close to 1068. Notice that, in order to find a sample size of 1068, we made $p ̂=0.5$ in $n=p ̂(1-p ̂)(\frac{z_{\frac{α}{2}}}{E})^2$. This value, $p ̂=0.5$, gives the highest sample size for a 95% confidence interval with a margin of error of 3%. Probably, a smaller sample is required. So, a sample of 1060 individuals is a good choice.

Work Step by Step

$level~of~confiance=(1-α).100$% $95$% $=(1-α).100$% $0.95=1-α$ $α=0.05$ $z_{\frac{α}{2}}=z_{0.025}$ If the area of the standard normal curve to the right of $z_{0.025}$ is 0.025, then the area of the standard normal curve to the left of $z_{0.025}$ is $1−0.025=0.975$ According to Table V, the z-score which gives the closest value to 0.975 is 1.96. Now, the sample size (no prior estimate of $p ̂$) : $E=0.03$ (margin of error of 3%) $n=0.25(\frac{z_{\frac{α}{2}}}{E})^2$ $n=0.25(\frac{1.96}{0.03})^2$ $n=1067.11$ Round up: $n=1068$
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