Name:
Assigned TF and Section time:
Statistics 100 Quiz 2
Wednesday 22 February 2012
This quiz has four questions and is worth 25 points; two of the questions are on the second
page.
The scatterplot below shows infant mortality (deaths in the first year of life per 1,000 births)
vs number of doctors per 100,000 members of the population for the 50 states plus the District of
Columbia. To the right of the plot is part of the Stata output for a least squares regression line fit
to the data.
4
6
8
10
12
Inf Mortality
200
400
600
800
Doctors per 100,000

infmortality 
Coef.
+
docsper100000

.0020496
_cons 
6.362203

1. The
r
2
for these data is 0.0194; what is the correlation coefficient?
[Answer]
Since the slope of the least squares regression line is positive (0
.
0020496), the correlation
coefficient is also positive, and therefore
r
=
√
r
2
=
√
0
.
0194 = 0
.
139.
2. Massachusetts has 469 doctors per 100,000 members of the population, and an observed
infant mortality 4.8 per 1,000 births. What is the predicted infant mortality for
Massachusetts and what is the error of the prediction (the term we called the residual).
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 Spring '11
 Grandal
 Statistics, Linear Regression, Regression Analysis, District of Columbia, squares regression line, MASSACHUSSETTS

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