ex2_2010 - Sociology 63993 Exam 2 March 26, 2010 I....

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Sociology 63993—Exam 2—Page 1 S o c i o l o g y 63993 E x a m 2 M a r c h 2 6 , 2 010 I. True-False. (20 points) Indicate whether the following statements are true or false. If false, briefly explain why. 1. A researcher has included extraneous variables in her model. Increasing her sample size will help with the problems that are created by doing this. 2. A researcher obtains the following: . estat ovtest Ramsey RESET test using powers of the fitted values of warm Ho: model has no omitted variables F(3, 2288) = 3.81 Prob > F = 0.0098 This suggests that she should add interaction terms to her model. 3. A researcher regresses income on the respondent’s race, years of education, IQ, and father’s education (i.e. the number of years of education the respondent’s father had). The estimated effect of father’s education is 0 and is statistically insignificant. This means that, in terms of their own income, respondents gain no benefit from having a better educated father. 4. In order to make interaction effects more interpretable, the dependent variable should be centered about its mean. 5. A researcher hypothesizes that informedness (measured on a 100 point scale) positively affects feelings of political efficacy for whites but has a negative effect for blacks. She obtains the following: β White = 0 β Inf = 7 β Inf*White = -5 β Inf and β Inf*White are both highly significant. The results support the researcher’s hypothesis. II. Path Analysis/Model specification (25 pts). A sociologist believes that the following model describes the relationship between X1, X2, X3, and X4. All her variables are in standardized form. The estimated value of each path in her model is included in the diagram.
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a. (5 pts) Write out the structural equation for each endogenous variable, using both the names for the paths (e.g. β 42 ) and the estimated value of the path coefficient. b. (10 pts) Part of the correlation matrix is shown below. Determine the complete correlation matrix. (Remember, variables are standardized. You can use either normal equations or Sewell Wright, but you might want to use both as a double-check.) | x1 x2 x3 x4 -------------+------------------------------------ x1 | 1.0000 x2 | 0.8000 1.0000 x3 | ? ? 1.0000 x4 | ? ? ? 1.0000 c. (5 pts) Decompose the correlation between X1 and X4 into Correlation due to direct effects Correlation due to indirect effects Correlation due to common causes d. (5 pts) Suppose the above model is correct, but instead the researcher believed in and estimated the following model: X2 X4 w What conclusions would the researcher likely draw? In particular, what would the researcher conclude about the effect of changes in X2 on X4? Discuss the consequences of this mis- specification, and in what ways, if any, the results would be misleading. Why would she make these mistakes? X1
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ex2_2010 - Sociology 63993 Exam 2 March 26, 2010 I....

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