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Statistics 21
Problems from past midterms: midterm 1
1.
(5 points) The quotations below are taken from an article in the San Francisco
Chronicle of May 31, 1989. The article begins:
“In recent years, statistics has shown that drinking a little alcohol is
good for your health.”
(a) Has this been shown on the basis of controlled experiments?
The article continues:
Some studies even suggest that moderate drinkers live longer than
people who don’t drink any alcohol.
Researchers refer to this phenomenon as the Ushaped alcoholmortal
ity curve. Nondrinkers and heavy drinkers are on opposite sides of
the curve with the highest death rates. Moderate drinkers fall in the
middle, with fewer early deaths from disease.
A new study of 7,700 British men, however, suggests that there’s more
to this curve than meets the eye.”
The article goes on to describe how the investigators in the new study analyzed the non
drinking group. These were the men who, at the time of the study, said they were not
drinking.
As the investigators expected from the earlier studies, the nondrinkers, as a
group, turned out to be not as healthy as the moderate drinkers. But the investigators
went further. They found that a large number of the men in the nondrinking group had
something in common. The investigators then removed the men with this common
characteristic from the nondrinking group. They found that, overall, the remaining
nondrinkers were just as healthy as the moderate drinkers.
(b) As a group, were the removed men more, or less, healthy than the moderate
drinkers?
(c) What was the common characteristic?
2.
(10 points) One number is missing from the data set below:
x
y
1
2
1
2
3
3
3
If possible, ±ll in the blank to make the correlation coef±cient equal to 0. If it is not pos
sible, say why not.
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3.
(10 points) An instructor gives two quizzes to the ten people in her course. On the frst
quiz, fve oF the people were above average; but on the second quiz, these people all
scored below average. The other fve people moved in the opposite direction. They were
all below average on the frst quiz, and above average on the second one.
(a) True or ±alse and explain:
This is an example oF the regression eFFect.
(b) The correlation coeFfcient between the scores on the two quizzes:
must be zero.
must be a positive number.
must be a negative number.
could be any oF the above, depending on
whether or not there are outliers in the data.
Check (√) one option. Explain your choice.
4.
(10 points) Here are the summary statistics For a large group oF male students at a
certain university.
Height: Average = 70.0 inches,
SD = 3.0 inches
Weight: Average = 162 pounds,
SD = 30 pounds
correlation coeFfcient = 0.50
The scatter diagram is Football shaped.
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This note was uploaded on 02/04/2011 for the course STAT 21 taught by Professor Anderes during the Fall '08 term at University of California, Berkeley.
 Fall '08
 anderes
 Statistics

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