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Unformatted text preview: CHAPTER 13 INFERENCE ABOUT COMPARING TWO POPULATIONS SECTIONS 12 MULTIPLE CHOICE QUESTIONS In the following multiplechoice questions, please circle the correct answer. 1. The expected value of the difference of two sample means equals the difference of the corresponding population means: a. only if the populations are normally distributed b. only if the samples are independent c. only if the populations are approximately normal and the sample sizes are large d. All of the above ANSWER: d 2. Two samples of sizes 25 and 35 are independently drawn from two normal populations, where the unknown population variances are assumed to be equal. The number of degrees of freedom of the equalvariances ttest statistic is: a. 60 b. 59 c. 58 d. 35 ANSWER: c 3. In constructing 95% confidence interval estimate for the difference between the means of two normally distributed populations, where the unknown population variances are assumed not to be equal, summary statistics computed from two independent samples are 179 180 Chapter Thirteen as follows: 50 1 = n , 175 1 = x , 5 . 18 1 = s , 42 2 = n , 158 2 = x , and 4 . 32 2 = s . The upper confidence limit is: a. 19.123 b. 28.212 c. 24.911 d. 5.788 ANSWER: b 4. In testing the difference between the means of two normally distributed populations, the number of degrees of freedom associated with the unequalvariances t test statistic usually results in a noninteger number. It is recommended that you: a. round up to the nearest integer b. round down to the nearest integer c. change the sample sizes until the number of degrees of freedom becomes an integer d. assume that the population variances are equal, and then use df = 2 2 1 + n n ANSWER: b 5. The quantity 2 p s is called the pooled variance estimate of the common variance of two unknown but equal population variances. It is the weighted average of the two sample variances, where the weights represent the: a. sample variances b. sample standard deviations c. sample sizes d. degrees of freedom for each sample ANSWER: d 6. Two independent samples of sizes 20 and 30 are randomly selected from two normally distributed populations. Assume that the population variances are unknown but equal. In order to test the difference between the population means, 2 1 μ μ , the sampling distribution of the sample mean difference, 2 1 x x , is: a. normally distributed b. t distributed with 50 degrees of freedom c. t distributed with 48 degrees of freedom d. Fdistributed with 19 and 29 degrees of freedom ANSWER: a 7. Two independent samples of sizes 40 and 50 are randomly selected from two populations to test the difference between the population means 2 1 μ μ . The sampling distribution of the sample mean difference 2 1 x x is: a. normally distributed b. approximately normal c. Student t distributed with 88 degrees of freedom Inference About Comparing Two Populations 181 d. None of the above ANSWER: b 8. Two independent samples of sizes 25 and 35 are randomly selected from two normal...
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 Spring '11
 ismailov
 Normal Distribution, Null hypothesis, UCL

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