Download Stat 3660: Final Exam “On my honor, I pledge that I have neither

Stat 3660: Final Exam
“On my honor, I pledge that I have neither given nor received help on this exam.”
Signature
(20 pts)
1. Write TRUE or FALSE.
(a) If your test score is higher than the class average, that means your score is better than
at least half of your classmates.
(b) The empirical rule says that approximately 95% of the observations in the sample lies
within one SD of the mean.
(c) Anecdotal studies have no control group.
(d) The alternative hypothesis says that the difference between the observed value and the
expected value is due to chance variation.
(e) Whenever an experiment has both treatment and control groups, the experiment is said
to be randomized controlled.
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(20 pts)
2. A political researcher investigated whether a higher percentage of Republicans than Democrats
are in favor of the death penalty. Out of 70 Republicans that he asked, 30% were in favor of
the death penalty. Out of 83 Democrats, 18% were in favor of the death penalty. Can the
observed difference be explained by chance variation, or are the differences too large for that?
Conduct a two-tailed test of significance. Write down all six steps and show all calculations.
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(20 pts)
3. Rats, like dogs, mark their territory using urine or other secretions. In a study of the
marking habits of rats, 20 male rats were placed in an environment containing female scents,
and another 20 male rats were placed in an environment containing male scents. The number
of markings made by each rat was recorded. The mean and standard deviations are:
Female scents
Male scents
Average
19.4
25.2
SD
2.75
3.40
Do the data provide sufficient evidence to indicate a difference in the mean number of markings
for those exposed to the female scent versus the male scent? Conduct a two-tailed test of
significance. Write down all six steps and show all calculations.
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(20 pts)
4. A survey of 2000 Americans compared their educational attainment by age. The data is
given in the following table:
Age
Less than 35 years old
35 to 65 years old
Over 65 years old
No bachelor’s degree
325
672
154
Bachelor’s degree or higher
245
528
76
Based on the data, are age and educational attainment associated or independent? Conduct
a chi-square test. (Write down H0 and H1 , show all calculations for expected counts and the
test statistic, and write down the P-value and conclusion.)
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(20 pts)
5. The output voltage for a certain electric circuit is specified to be 110. A sample of seven
independent readings on the voltage of this circuit yielded the following:
112, 125, 110, 115, 124, 111, 115
(a) Calculate the standard deviation (step-by-step, using 3-column layout like it is done in
the course pack).
(b) Calculate a 95% confidence interval for the average output voltage of the circuit.
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