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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.
TrueFalse.
(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 doublecheck.)

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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 Spring '11
 RichardWilliams
 Sociology

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