Statistics Chapter 9 Questions & Answers

Statistics Chapter 9 Questions & Answers A 95% confidence interval for the ages of six consecutive presidents at their inaugurations is about (48.4, 54.2). Either interpret the interval or explain why it should not be interpreted. - ANSWER: It should not be interpreted. The data are not a random sample and so inference based on a confidence interval is not possible. A 95% confidence interval is equivalent to which of the following hypothesis tests? - ANSWER: A two-tailed test with a significance level of 0.05 A biologist is studying the effects that applying insecticide to a fruit farm has on the local bat population. She collects 23 bats and finds the mean weight of this sample to be 503.4 grams. Assuming the selected bats are a random sample, she concludes that because the sample mean is an unbiased estimator of the population mean, the mean weight of bats in the population is also 503.4 grams. Explain why this is an incorrect interpretation of an unbiased estimator. - ANSWER: Having an "unbiased" estimator means that the mean of the means of all possible samples of the same size would be the same as the population mean. A confidence interval answers which of the following questions? - ANSWER: What is the estimated value and how much uncertainty does one have in this estimate? A confidence interval communicates an estimate of the mean and also which of the following? - ANSWER: A measure of one's uncertainty in the estimate A human resources manager for a large company takes a random sample of 50 employees from the company database. She calculates the mean time that they have been employed. She records this value and then repeats the process: She takes another random sample of 50 names and calculates the mean employment time. After she has done this 1000 times, she makes a histogram of the mean employment times. Is this histogram a display of the population distribution, the distribution of a sample, or the sampling distribution of means? - ANSWER: The histogram is a display of the sampling distribution of means.