ex1_2012ak - Sociology 63993 Exam 1 Answer Key I...

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Sociology 63993—Exam 1 Answer Key —Page 1 Sociology 63993 Exam 1 Answer Key February 17, 2012 I. True-False. (20 points) Indicate whether the following statements are true or false. If false, briefly explain why. 1. Cohen and Cohen’s dummy variable adjustment method is useful when variables like gender or age have missing values. False. The method should not be used when values exist but are not known (and values for gender and age surely exist). The method can be useful when values don’t exist, e.g. father’s education is missing because there is no father in the family. 2. R 2 is biased downwards. False. It is biased upwards. Sampling error will always cause R 2 to be greater than zero, i.e. even if no variable has an effect R 2 will be positive in a sample. When there are no effects, across multiple samples you will see estimated coefficients sometimes positive, sometimes negative, but either way you are going to get a non-zero positive R 2 . Further, when there are many Xs for a given sample size, there is more opportunity for R 2 to increase by chance. Adjusted R 2 corrects for this bias. 3. The more “tolerant” a variable is (i.e. the less highly correlated it is with the other IVs), the smaller its unique contribution to R 2 will be. False. The more tolerant a variable is, the more unique (and higher) its contribution to R 2 will be. You can see this via such formulas as 22 2 2 2 2 * (1 ) * k kk k YH YG k X G k k sr R R b R b Tol ′′ = −= = 4. When you have more than one independent variable, random measurement error can cause coefficients to be biased either upward or downward. True. In bivariate regression, the bias will be downward, but once you have more than one independent variable the bias can go in either direction. 5. A Durbin-Watson statistic of 4 or greater indicates that the case is an extreme outlier. False. The Durbin-Watson statistic checks for serial correlation. II. Short answer. Discuss all three of the following problems. (15 points each, 45 points total.) In each case, the researcher has used Stata to test for a possible problem, concluded that there is a problem, and then adopted a strategy to address that problem. Explain (a) what problem the researcher was testing for, and why she concluded that there was a problem, (b) the rationale behind the solution she chose, i.e. how does it try to address the problem, and (c) one alternative solution she could have tried, and why. (NOTE: a few sentences on each point will probably suffice – you don’t have to repeat everything that was in the lecture notes.)
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Sociology 63993—Exam 1 Answer Key —Page 2 II-1. . use "http://www.nd.edu/~rwilliam/stats3/statafiles/rwm11.dta", clear (German Health Care Panel Data, Riphahn Wambach Million (2003), Greene (2007)) . reg newhsat female age handdum educ married working if year==1984 Source | SS df MS Number of obs = 3874 -------------+------------------------------ F( 6, 3867) = 141.19 Model | 4483.9589 6 747.326483 Prob > F = 0.0000 Residual | 20468.7796 3867 5.29319359 R-squared = 0.1797 -------------+------------------------------ Adj R-squared = 0.1784 Total | 24952.7385 3873 6.44274168 Root MSE = 2.3007 ------------------------------------------------------------------------------ newhsat | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- female | -.186618 .0870046 -2.14 0.032 -.3571973 -.0160387 age | -.0388289 .0035637 -10.90 0.000 -.0458159 -.031842 handdum | -2.341489 .1236374 -18.94 0.000 -2.58389 -2.099088 educ | .1089876 .0173546 6.28 0.000 .0749626 .1430125 married | .2048268 .0918166 2.23 0.026 .0248133 .3848402 working | .2955985 .0912629 3.24 0.001
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ex1_2012ak - Sociology 63993 Exam 1 Answer Key I...

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