518 Statistical Methods
determine whether the delivery pro-
cess is in control. If not, suggest some
special causes that might exist.
c. Report your results and save your
changes to the workbook.- A steel sheet manufacturer is concerned
about the number of defects, such as
scratches and dents, that occur as the
sheet is made. In order to track defects,
10-foot lengths of sheet are examined at
regular intervals. For each length, the
number of defects is counted. Analyze
these data to determine whether the pro-
cess is in control.
a. Open the Sheet workbook from the
Chapter12 folder and save the fi le as
Sheet Control Chart.
b. Determine whether the process is in
control. If it is not, suggest some spe-
cial causes that might exist.
c. Save your changes to the workbook
and write a report summarizing your
conclusions. - A fi rm is concerned about safety in its
workplace. This company does not con-
sider all accidents to be identical. Instead,
it calculates a safety index, which
assigns more importance to more serious
accidents. Examine the data from their
study and perform the following analysis:
a. Open the Safety workbook from the
Chapter12 folder and save it as Safety
Control Chart.
b. Construct a C chart for the data to de-
termine whether safety is in control at
this fi rm.
c. Save your changes to the workbook
and report your conclusions. - A manufacturer subjects its steel bars
to stress tests to be sure they are up to
standard. Three bars were tested in each
of 23 subgroups. The amount of stress
applied before the bar breaks is recorded
by the manufacturer.
a. Open the Stress workbook from the
Chapter12 folder and save it as Stress
Control Chart.
b. Create a range chart and a x chart to
determine whether the production
process is in control. If it is not, what
factors might be contributing to the
lack of control?
c. Report your results, saving your
changes to the workbook.- A steel rod manufacturer has contracted
to supply rods 180 millimeters in length
to one of its customers. Because the cut-
ting process varies somewhat, not all
rods are exactly the desired length. Five
rods were measured from each of 33
subgroups during a week. Analyze these
data to determine whether the process is
in control.
a. Open the Rod workbook from the
Chapter12 folder and save it as
Rod Control Chart.
b. Create range and x charts to deter-
mine whether the cutting process is in
statistical control.
c. Save your changes to the workbook
and write a report summarizing your
conclusions. - An amusement park sampled customers
leaving the park over an 18-day period.
The total number of customers and the
number of customers who indicated
they were satisfi ed with their experience
in the park were recorded in an Excel
workbook. You‘ve been asked to analyze
these data to determine whether the
percentage of satisfi ed customers is in
statistical control.
a. Open the Satisfy workbook from the
Chapter12 folder and save it as Satisfy
Control Chart.
b. Create the appropriate control chart for
the percentage of satisfi ed customers.
Is there any indication that the process