486 Statistical Methods
a. Open the Oil workbook from the
Chapter11 folder and save it as Oil
Forecasts.
b. Restructure the data in the worksheet
into a two-way table. Create a line
plot of the production values in the
table using a separate line for each
year. Describe the seasonal nature of
cottonseed oil production.
c. Smooth the production data using a
value of 0.15 for all three smoothing
factors. Forecast the values 12 months
into the future. What are your projec-
tions and your upper and lower limits
for 1996?
d. Adjust the production data for the
seasonal effects. Is there evidence that
the adjusted production values have
increased over the four-year period?
Test your assumption by performing
a linear regression of the adjusted
values on the month number (1–48).
Is the regression signifi cant at the
5% level?
e. Save your changes to the workbook
and write a report summarizing your
conclusions.- The Bureau of Labor Statistics records
the number of work stoppages each
month that involve 1000 or more work-
ers in the period. Are such work stop-
pages seasonal in nature? Are there
more work stoppages in summer than
in winter?
a. Open the Stoppage workbook from
the Chapter11 folder and save it as
Stoppage Analysis.
b. Restructure the data in the Work Stop-
page worksheet into a two-way table,
with each year in a separate row and
each month in a separate column.
c. Use the two-way table to create a box-
plot and line plot of the work stop-
page values. Which months have the
highest work stoppage numbers? Do
work stoppages occur more often in
winter or in summer?
d. Adjust the work stoppage values
assuming a 12-month cycle. Is there
evidence in the scatterplot that the
adjusted number of work stoppages
has decreased over the past decade?
e. Smooth adjusted values using one-
parameter exponential smoothing.
Use a value of 0.15 for the smoothing
parameter.
f. Save your changes to the workbook.
Summarize your fi ndings regarding
work stoppages of 1000 or more work-
ers. Are they seasonal? Have they de-
clined in recent years? Use whatever
charts and tables you created to sup-
port your conclusions.- The Jobs workbook contains monthly
youth unemployment rates from 1981 to
1996. Analyze the data in the workbook
and try to determine whether unemploy-
ment rates are seasonal.
a. Open the Jobs workbook from the
Chapter11 folder. Save it as Jobs
Analysis.
b. Restructure the data in the Youth
Unemployment worksheet into a two-
way table, with each year in a separate
row and each month in a separate
column.
c. Create a spaghetti plot of the unem-
ployment values.
d. Create a boxplot of youth unemploy-
ment rates. Is any pattern apparent in
the boxplot?
e. Adjust the unemployment rates as-
suming a 12-month cycle. Is there
evidence in the chart that youth un-
employment varies with the season?
f. Save your changes to the workbook
and write a report summarizing your
observations.