1.The sample mean is an unbiased estimator for
the population mean. This means:
 The sample mean always equals the population mean.
 The average sample mean, over all possible samples, equals the
population mean.
 The sample mean will only vary a little from the population
mean.
 The sample mean has a normal distribution.
2.Which of the following statements is
CORRECTabout the sampling distribution of the
sample mean:
 The standard error of the sample mean will decrease as the
sample size increases.
 The standard error of the sample mean is a measure of the
frequency among repeated samples.
 The sampling distribution does not always follow a normal
distribution even when n (the sample size) is
large.
 The standard error of the sample mean will increase as the
sample size increases.
3.A simple random sample (SRS) is taken from a
population. Which statement is CORRECT?
 µ is an estimate of xbar; σ is an estimate of s.
 xbar is an estimate of µ; s is an estimate of σ.
 µ is an estimate of xbar; s is an estimate of the standard
deviation of the sample mean.
 µ is an estimate of s; σ is an estimate of xbar
4Which of the following statements about
confidence intervals is CORRECT? A
confidence interval is:
 The estimate plus or minus the tscore.
 The parameter plus or minus the tscore times the standard
error.
 The estimate plus or minus the margin of error.
 None of the above.
5.Which of the following statements about
confidence intervals is WRONG?
 If we keep the sample size fixed, the confidence interval gets
wider as we increase the confidence coefficient.
 A confidence interval for a mean always contains the sample
mean.
 If we keep the confidence coefficient fixed, the confidence
interval gets narrower as we increase the sample size.
 If the standard error increases, the confidence interval
decreases in width.
6.Which of the following statements is
CORRECT?
 An extremely small pvalue indicates that the actual data
differs markedly from that expected if the null hypothesis were
true.
 The pvalue measures the probability that the hypothesis is
true.
 The larger the pvalue, the stronger the evidence against the
null hypothesis
 The pvalue measures the probability that the sample mean is
more than the population mean.
7.The average time it takes for a person to
experience pain relief from aspirin is 25 minutes. A new ingredient
is added to help speed up relief. Let µ denote the average time to
obtain pain relief with the new product. An experiment is conducted
to verify if the new product is better. What are the null and
alternative hypotheses?
 H_{0}: µ = 25
H_{A}: µ = 25
 H_{0}: µ = 25
H_{A}: µ <
25
 H_{0}: µ < 25
H_{A}: µ = 25
d. All of the
above is correct since both the null and alternative hypotheses can
be set up arbitrarily.
8.Suppose you are conducting a two sample
significance testing. The null hypothesis states that
 The samples come from populations with different means
 The samples have the same sample mean
 The samples have very different sample means
 The samples come from populations with the same mean
9.In a random sample of 100 individuals, 12 are
lefthanded. Which of the following is a plausible 95% confidence
interval for the proportion of lefthanded people in the
population?
 0.056 to 0.184
 0.037 to 0.103
 0.056 to 0.084
 0.120 to 0.240
DEFINITION:5 points each: write a one or two
sentence definition of each term.
 of Error
 Error
 Alternative Hypothesis
 Significance
SHORT ANSWER:6 points each: write your answer
in the space following each question.
 Bush believed that “No Child Left Behind”
improves test scores of school children. You have data before and
after the implementation of the program. Using simple regression
analysis, how would you test for the effect of the policy? Identify
the dependent variable and the independent variable. Define the
null and alternative hypotheses in words and in statistical
notation.
 government’s Current Population Survey
interviewed more than 131,000 people aged between 25 and 65, who
are in the labor force, in March 2002. The mean income of this
group was $44,776. median income for the same
group was $35,680. Is each of the bold numbers a
parameter or a statistic? Explain.
 Gallup Poll in November 2002 found that 51% of the people in
its sample said “Yes” when asked, “Would you like to lose weight?”
Gallup announced: For results based on the total sample of national
adults, one can say with 95% confidence that the margin of sampling
error is +3 percentage points.”
 What does it mean to say that we have “95% confidence” in this
interval?
 What is the 95% confidence interval for the percent of all
adults who want to loose weight?
 asked why statistical significance appears so
often in research reports, a student says, “Because saying that
results are significant tells us that they cannot easily be
explained by chance variation alone.” Do you think this statement
is essentially correct? Explain your answer.

 time taken for Leslie to travel home to school is
distributed normally with a mean of 70 minutes and a standard
deviation of 10 minutes.
 What percentage of the time will the trip take less than 60
minutes?
 Is 100 minutes an unusually long commuting
trip? What percentage of the time will this occur?
INTERPRETATION OF COMPUTER OUTPUT (10 points
each).
 The following gives the results of the regression output from
Stata.
Dependent variable: travel time to
work in minutes.
Independent variable: a disability
affecting work indicator

TRAVELTIME  Coef. Std.
Err. t P>t Beta
+
Work
Disability  1.595 2.299 0.694 0.488 0.023
_cons  21.754 .727 29.904 0.000

For the following questions, please use 3 places of decimal.
 What value does the work disability variable take if you are
not disabled?
 What is the average travel time to work for a person without a
disability?
 What is the difference between the time traveled by disabled
persons and those who are not disabled?
 What is the average travel time to work for disabled
persons?
 Are disabled people significantly different from nondisabled
people in the time taken to reach work? Explain.
 The following gives the results of the regression output from
STATA.
Dependent variable: Wage and Salary
Income.
Independent variable: a disability
affecting work indicator

INCWS  Coef. Std.
Err. t P>t Beta
+
Work
Disability 9303.723 4475.500 2.079 0.038 0.070
_cons
 37931.813 1416.073 26.787 0.000

 Write the regression equation for the above output.
 What information does the constant give you?
 What information does the slope give you?
 Write the null and alternative hypotheses to test whether or
not disabled people earn less than nondisabled people.
 At the 5% significance level, do disabled people earn less than
nondisabled people?
 At the 1% significance level, do disabled people earn less than
nondisabled people?