REAL STATISTICS REAL DECISIONS Putting it all together 412 CHAPTER 7 Hypothesis Testing with One Sample The charts show results of studies on four-year colleges in the United States. You want to portray your college in a positive light for an advertising campaign designed to attract high school students. You decide to use hypothesis tests to show that your college is better than the average in certain aspects. EXERCISES 1. What Would You Test? What claims could you test if you wanted to convince a student to come to your college? Suppose the student you are trying to convince is mainly concerned with (a) affordability, (b) having a good experience, and (c) graduating and starting a career. List one claim for each case. State the null and alternative hypotheses for each claim. 2. Choosing a Random Sample Classmates suggest conducting the following sampling techniques to test various claims. Determine whether the sample will be random. If not, suggest an alternative. (a) Survey all the students you have class with and ask about the average time they spend daily on different activities. (b) Randomly select former students from a list of recent graduates and ask whether they are employed. (c) Randomly select students from a directory, ask how much debt money they borrowed to pay for college this year, and multiply by four. 3. Supporting a Claim You want your test to support a positive claim about your college, not just fail to reject one. Should you state your claim so that the null hypothesis contains the claim or the alternate hypothesis contains the claim? Explain. 4. Testing a Claim You want to claim that students at your college graduate with an average debt of less than $25,000. A random sample of 40 recent graduates has a mean amount borrowed of $23,475 and a standard deviation of $8000. At a = 0.05, is there enough evidence to support your claim? 5. Testing a Claim You want to claim that your college has a freshman retention rate of at least 80%. You take a random sample of 60 of last year’s freshmen and find that 54 of them still attend your college. At a = 0.05, is there enough evidence to reject your claim? 6. Conclusion Test one of the claims you listed in Exercise 1 and interpret the results. Discuss any limits of your sampling process. Percent College Success x 0 20 40 60 80 100 Freshman retention rate 4-year graduation rate 5-year graduation rate 6-year graduation rate Recent graduate employment rate 94.9% 76.2% 43.7% 58.7% 62.4% Amount College Cost x Annual tuition, public, In-state Annual tuition, public, Out-of-state Annual tuition, private Total amount borrowed Total grant and scholarship aid 0 10,000 20,000 30,000 $13,690 $30,062 $35,087 $9687 $21,184 Average (in hours) Student Daily Life x Sleeping Leisure and sports Educational activities Working Traveling Dining Other 0 2 4 6 8 10 8.8 4.0 3.5 2.3 1.4 1.0 3.0
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