Stats 350 Exam 1 solutions

Stats 350 Exam 1 solutions - Stat 350 Winter 2008 Exam 1...

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Stat 350 Winter 2008 Exam 1 Solutions 1. a. What type of study is this? (circle one) Observational Experiment b. Which of the following interpretations of the researchers’ finding (higher salary for the internship group on average) do you think is the most appropriate? Circle the one best answer. ii. There could be a confounding variable (for example, student major) that explains the difference in mean salary between the internship and no internship groups. c. Suppose one of the researchers expressed concern that the survey respondents might have overstated their salaries (i.e. reported a higher salary than they actually earn). This would be an example of which type of bias? Response bias 2. Is it appropriate to say that the distribution of responses is skewed right? Explain in one simple sentence. This is a bar graph, not a histogram. Or the variable ‘favorite sport’ is categorical, not quantitative. 3. a. What is the probability that a randomly selected mall shopper would prefer an electronic gift? P(Prefer Electronic Gift) = 1500/2000 = 0.75 b. What is the probability that a randomly selected mall shopper is under 30 years of age? P(Under 30) = 800/2000 = 0.40 c. Suppose a mall shopper is under 30 years of age, what is the probability that they would prefer an electronic gift? P(Prefer Electronic Gift | Under 30) = 600/800 = 0.75 d. Based on these results, are age category and gift-receiving preference independent for this population? Yes Give clear support for your answer. P(Prefer Electronic Gift | Under 30) = P(Prefer Electronic Gift) 0.75 = 0.75 Or P(Under 30 | Prefer Electronic Gift) = P(Under 30) 600/1500 (=0.40) = 0.40 Or P(Under 30 and Prefer Electronic Gift) = P(Under 30) P(Prefer Electronic Gift) 600/2000 (=0.30) = (0.40)(0.75) = 0.30 4. a. What proportion of the sampled students was concerned about the decision? =126/200 = 0.63 p ˆ b. What is the corresponding standard error of the estimate in part (a)?
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Stats 350 Exam 1 solutions - Stat 350 Winter 2008 Exam 1...

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