Chapter 7: Problem 105
Suppose that, when taking a random sample of 4 from 123 women, you get a mean height of only 60 inches ( 5 feet). The procedure may have been biased. What else could have caused this small mean?
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Chapter 7: Problem 105
Suppose that, when taking a random sample of 4 from 123 women, you get a mean height of only 60 inches ( 5 feet). The procedure may have been biased. What else could have caused this small mean?
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The website www.mlb.com compiles statistics on all professional baseball players. For the 2017 season, statistics were recorded for all 663 players. Of this population, the mean batting average was \(0.236\) with a standard deviation of \(0.064\). Would it be appropriate to use this data to construct a \(95 \%\) confidence interval for the mean batting average of professional baseball players for the 2017 season? If so, construct the interval. If not, explain why it would be inappropriate to do so.
A double-blind study using random assignment was done of pregnant women in Denmark. Women were given fish oil or a placebo during pregnancy. Their children were followed during the first 5 years of life to see if they developed asthma. The results are summarized in the table. (Bisgaard et al., "Fish Oil-Derived Fatty Acids in Pregnancy and Wheeze and Asthma in Offspring," New England Journal of Medicine, vol. \(375: 2530-2539 .\) doi: \(10.1056 /\) NEJMoa 1503734 ) $$\begin{array}{|lcc|}\hline \text { Developed asthma } & \text { Fish Oil } & \text { Placebo } \\\\\hline \text { Yes } & 58 & 83 \\ \hline \text { No } & 288 & 266 \\\\\hline\end{array}$$ a. Calculate and compare the percentages of children who developed asthma in the fish oil group and in the placebo group. b. Check that the conditions for using a two-population confidence interval hold. c. Find the \(95 \%\) confidence interval for the difference in the proportion of children who develop asthma in the two groups. Based on your confidence interval, can we conclude that there is a difference in the population proportions?
Explain the difference between sampling with replacement and sampling without replacement. Suppose you have the names of 10 students, each written on a 3 -inch by 5 -inch notecard, and want to select two names. Describe both procedures.
In the 2018 study Closing the STEM Gap, researchers wanted to estimate the percentage of middle school girls who planned to major in a STEM field. a. If a \(95 \%\) confidence level is used, how many people should be included in the survey if the researchers wanted to have a margin of error of \(3 \%\) ? b. How could the researchers adjust their margin of error if they want to decrease the number of study participants?
Suppose that, when taking a random sample of three students' GPAs, you get a sample mean of \(3.90 .\) This sample mean is far higher than the collegewide (population) mean. Does that prove that your sample is biased? Explain. What else could have caused this high mean?
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