Chapter 9 Answers
9.1, 9.2, 9.3, 9.7, 9.8, 9.10
1.
As explained in the text, potential threats to external validity arise from differences between the
population and setting studied and the population and setting of interest. The statistical results based
on New York in the 1970’s are likely to apply to Boston in the 1970’s but not to Los Angeles in the
1970’s. In 1970, New York and Boston had large and widely used public transportation systems.
Attitudes about smoking were roughly the same in New York and Boston in the 1970s. In contrast,
Los Angeles had a considerably smaller public transportation system in 1970. Most residents of Los
Angeles relied on their cars to commute to work, school, and so forth.
The results from New York in the 1970’s are unlikely to apply to New York in 2002. Attitudes
towards smoking changed significantly from 1970 to 2002.
2.
(a) When
Y
i
is measured with error, we have
or
Substituting the 2nd
equation into the regression model
,
ii
i
YYw
.
ii i
01
i
YX
i
i
u
gives
,
i
Xu
Yw
i
i
w
or
Thus
.
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 Summer '09
 Megerdichian
 Econometrics, Normal Distribution, Regression Analysis, Errors and residuals in statistics, Yi Yi wi

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