Question: Your firm is having a quality problem with the production of plastic automotive parts: There are too many defectives. One of your engineers thinks the reason is that the temperature of the process is not controlled carefully enough. Another engineer is sure that it is the assembly line being shut down too often for unrelated reasons. You have decided to analyze the problem and have come up with figures for the percent defective each day recently, the standard deviation of temperature measured hourly each day (as a measure of temperature control), and the number of assembly line stoppages each day. The raw data set is shown in Table.
a. Find the correlation of the defect rate with the temperature variability.
b. Find the correlation of the defect rate with stoppages.
c. Which possible cause, temperature variability or stoppages, accounts for more of the variation in defect rate from day to day? How do you know?
d. Test each of these correlations for statistical significance.
e. Draw a scatterplot of defect rate against stoppages. Write a brief paragraph interpreting the scatterplot and correlation.
f. Draw a scatterplot of defect rate against temperature variability. Write a brief paragraph interpreting the scatterplot and correlation.
g. Write a paragraph summarizing what you have learned and proposing a plan for action.
