statsexam1f06sol

statsexam1f06sol - Economic Statistics Exam 1 September 26,...

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Economic Statistics Exam 1 SOLUTION KEY September 26, 2006 This exam contains fifteen short answer questions ( worth 4 points each ) and four long answer questions ( worth 15 points each ) . Please answer in the space provided; if you need more room, indicate clearly that the answer is continued on the back of the page. In all problems where you need to make a calculation, simplify your answer as much as possible. Show your work clearly to be eligible for partial credit. Short Questions ( 4 points apiece ) 1. Professor Smith gives an exam to a small class of students. The scores on the exam were: 68, 72, 83, 85, 86, 88, 88, 91, and 97. Give me the five - number summary of this distribution. Min: 68 Lower quartile: 83 ( other acceptable answers ) Median: 86 Upper quartile: 88 ( other acceptable answers ) Max: 97 2. Suppose that you have a Stata database containing the variables cancer and smoking . Write the Stata command that would output descriptive statistics for smoking , including the mean, variance, and quartiles. summarize smoking, detail 3. When constructing a perfect scatterplot , you are asked to draw the line that best explains the relationship between two variables, X and Y . How do you determine the location and slope of this line? Location: goes through ! X , Y " Slope: equal to r xy ! s y s x = s xy s x 2
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Econ 400 Midterm 1, page 2 of 9. 4. The following graph came from a news article on CNN.com. What is the most serious problem with this graph? There is an inconsistency: it compares full - year sales in 2001, 2002, 2003, 2004, and 2005 to sales in the first eight months of 2006. 5. When a healthy, sexually active couple is trying to get pregnant, there is a roughly 0.25 chance of conceiving in any given month. Assuming that these chances are independent from one month to the next, what is the probability that a couple gets pregnant within three months? Let s call A 1 the event that the couple conceives in the first month, A 2 for the second, and A 3 for the third. Then note that: P ! A 1 ! A 2 ! A 3 " = 1 " P !# not A 1 $ # # not A 2 $ # # not A 3 $" = 1 " P !# not A 1 $" $ P !# not A 2 $" $ P !# not A 3 $" # since independent $ = 1 " # 0 . 75 $ 3
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Econ 400 Midterm 1, page 3 of 9. 6. The experiment in this problem is looking at the contents of a randomly selected student at UNC. The event A is that the iPod contains music by Weird Al Yankovic , and the event B is that the iPod contains music by Chamillionaire. Use the following table ( containing the joint probabilities ) to determine if these events are independent, and explain your reasoning. Contains
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statsexam1f06sol - Economic Statistics Exam 1 September 26,...

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