Quality Associates, Inc., a consulting firm, advises its clients about sampling and

statistical procedures that can be used to control their manufacturing processes.

In one particular application, a client gave Quality Associates a sample of 800

observations taken during a time in which that client's process was operating

satisfactorily.

? The sample standard deviation for these data was .21; hence, with so much data, the

population standard deviation was assumed to be .21.

? Quality Associates then suggested that random samples of size 30 be taken periodically

to monitor the process on an ongoing basis.

? By analyzing the new samples, the client could quickly learn whether the process was

operating satisfactorily.

When the process was not operating satisfactorily, corrective action could be taken to

eliminate the problem.

? The design specification indicated the mean for the process should be 12.

? The hypothesis test suggested by Quality Associates follows.

Corrective action will be taken any time H 0 is rejected.

The following samples were collected at hourly intervals during the first day of operation

of the new statistical process control procedure. These data are available in the data set

Quality.

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