statsexam1f11sol

# statsexam1f11sol - Economic Statistics Exam 1 Last name...

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Economic Statistics Exam 1 Last name: September 22, 2011 First name: Class time: 11:00-12:15 or 12:30-1:45 PID: Please sign that you abide by the honor pledge: This exam contains twelve short answer questions (worth 6 points each) and three long answer questions (worth 10 points each). Please answer in the space provided. In all problems where you need to make a calculation, simplify your answer as much as possible. Technique is important, so show your work clearly. Short Questions (6 points apiece) 1. What is the approximate relationship between the range and standard deviation of a variable? The standard deviation is approximately ¼ of the range. 2. The variable X comes from a distribution with a mean of 29 and a variance of 4 . If Mr. Smith’s value of X equals 34, then his standardized value is what? The standardized value is calculated as z = ( x x )/ s x . Note that s x = s x 2 = 4 = 2 . In this case, the answer is z = (34 29)/2 = 2.5 . 3. What does it mean for events A and B to be “statistically independent”, and what does it mean for them to be “mutually exclusive”? Two events are statistically independent if knowing the outcome of one does not cause us to revise our expectations about the likeliness of the other; P [ A | B ] = P [ A ] . Two events are mutually exclusive if they cannot both occur simultaneously; P [ A and B ] = 0 . 4. What is the rule of thumb for determining whether the correlation between two variables is a “meaningful relationship” or due to chance? A “meaningful relationship” exists if r xy > 2 n .

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Econ 400 Midterm 1, page 2 of 7. 5. Suppose that Stata gives me the following information about my sample:
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## This note was uploaded on 01/11/2012 for the course ECON 400 taught by Professor Turchi during the Fall '08 term at UNC.

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statsexam1f11sol - Economic Statistics Exam 1 Last name...

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