midterm_au05_answers

midterm_au05_answers - Sociology 549, Paul von Hippel,...

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Sociology 549, Paul von Hippel, Autumn 2005 Note : This is an edited exam whose answer key differs slightly from the one used in Autumn 2005 Midterm (40 points): ANSWER KEY Time allotted: 90 minutes. Be concise. Stick to concepts that were covered in class. General grading guidelines: Don’t be fussy about rounding error. If answer A is wrong, but answer B is consistent with answer A, only deduct points for answer A. 1. (7½ points) Recently the New York Times ran a story on apartment prices in Manhattan. a. (3½ points) If you had to guess, what do you think the distribution of Manhattan apartment prices would look like? Sketch the distribution and describe its shape. Why do you think it has this shape? 1 point for drawing a right-skewed distribution. ½ point for labeling the axes (1/4 point for each axis). ½ point for saying it’s skewed; another ½ point for saying the skew is positive. (Full credit for the description if it agrees with the sketch, even if the sketch is wrong.) 1 point for saying the skew comes from the fact that there’s a minimum possible price (maybe zero) but no maximum possible price. b. (2 points) In the Times story, the headline said that the average price was a million dollars. But the fifth paragraph said that the median price was $500,000. Why might the average be so much larger than the median? The average is sensitive to extreme values (½ point), but the median is not (½ point). If a few apartments had very high prices—and the skew suggests they do—this would pull up the average but not the median. (1 point)
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c. (2 points) Suppose you wanted to buy an apartment in Manhattan. Your realtor shows you an apartment priced at $750,000. Are most of the apartments in Manhattan cheaper than this, or more expensive? How do you know? Be explicit. Most of the apartments are cheaper than $750,000. (1 point) The median price is $500,000 (½ point), so at least half of the apartment are priced at $500,000 or less (½ point)
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2. (7½ points) Over the past month, the University of Akron polled Ohio voters about Issue 4, a constitutional amendment that would change the way Ohio draws legislative boundaries. In a simple random sample of 409 likely voters, 178 said that they favored Issue 4; the other respondents opposed it.
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midterm_au05_answers - Sociology 549, Paul von Hippel,...

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