A quality control chart has been maintained for a

Chapter 15, Problem 50E

(choose chapter or problem)

A quality control chart has been maintained for a measurable characteristic of items taken from

a conveyor belt at a fixed point in a production line. The measurements obtained today, in order

of time, are as follows:

             

                          68.2   71.6   69.3   71.6   70.4   65.0   63.6   64.7

                          65.3   64.2   67.6   68.6   66.8   68.9   66.8   70.1

a Classify the measurements in this time series as above or below the sample mean and

determine (using the runs test) whether consecutive observations suggest lack of stability

in the production process.

b Divide the time period into two equal parts and compare the means, using Student’s t test.

Do the data provide evidence of a shift in the mean level of the quality characteristics?

Explain.