Sociology 63993—Exam 1 Answer Key —Page 1
Exam 1 Answer Key
February 17, 2012
(20 points) Indicate whether the following statements are true or false. If false, briefly explain why.
Cohen and Cohen’s dummy variable adjustment method is useful when variables like gender or age have missing
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.
is biased downwards.
False. It is biased upwards. Sampling error will always cause R
to be greater than
zero, i.e. even if no variable has an effect R
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
. Further, when there are many Xs for a given sample size, there is more opportunity
to increase by chance. Adjusted R
corrects for this bias.
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
False. The more tolerant a variable is, the more unique (and higher) its contribution to
will be. You can see this via such formulas as
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.
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.
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.)