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.

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Quality
Associates
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.
Ho: μ = 12
Ha: μ # 12
Corrective action will be take any time H0 is rejected.
The following samples were collected at hourly intervals
during the first day of operation of the new statistical process
control procedure.
Transcribed Image Text:Quality Associates 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. Ho: μ = 12 Ha: μ # 12 Corrective action will be take any time H0 is rejected. The following samples were collected at hourly intervals during the first day of operation of the new statistical process control procedure.
Sample 1 Sample 2 Sample 3 Sample 4
11.55 11.62 11.91
12.02
11.62 11.69 11.36
12.02
11.52 11.59 11.75
12.05
11.75 11.82 11.95
12.18
11.90
11.97 12.14
12.11
11.64 11.71 11.72
12.07
11.80 11.87 11.61 12.05
12.03 12.10
11.85
11.64
11.94 12.01 12.16 12.39
11.92
12.13 12.20 12.12
11.99 11.91 11.65
12.11
12.09
12.16
11.61 11.90
11.93 12.00 12.21 12.22
12.21 12.28 11.56
11.88
12.32
11.93 12.00 12.01
12.39 11.95 12.03
12.35
11.85 11.92 12.06 12.09
0
11.76 11.83 11.76 11.77
12.16 12.23 11.82 12.20
11.77 11.84 12.12 11.79
12.00 12.07 11.60 12.30
12.04 12.11 11.95 12.27
11.98 12.05 11.96 12.29
12.30 12.37 12.22 12.47
12.18 12.25 11.75 12.03
11.97 12.04 11.96 12.17
12.17 12.24 11.95 11.94
11.85 11.92 11.89 11.97
12.30 12.37 11.99 12.23
12.15 12.22 11.93 12.25
Managerial Report:
1) Compute the standard deviation for each of the four samples.
Does the assumption of .21 for the population standard
deviation appear reasonable?
2) Compute limits for the sample mean around u-12 such that,
as long as a new sample mean is within those limits, the process
will be considered to be operating satisfactorily. If sample mean
exceeds the upper limit or if sample mean is below the lower
limit, corrective action will be taken. These limits are referred
to as upper and lower control limits for quality control
purposes.
3) Discuss the implications of changing the level of significance
to a larger value. What mistakes or error could increase if the
level of significance in increased?
Transcribed Image Text:Sample 1 Sample 2 Sample 3 Sample 4 11.55 11.62 11.91 12.02 11.62 11.69 11.36 12.02 11.52 11.59 11.75 12.05 11.75 11.82 11.95 12.18 11.90 11.97 12.14 12.11 11.64 11.71 11.72 12.07 11.80 11.87 11.61 12.05 12.03 12.10 11.85 11.64 11.94 12.01 12.16 12.39 11.92 12.13 12.20 12.12 11.99 11.91 11.65 12.11 12.09 12.16 11.61 11.90 11.93 12.00 12.21 12.22 12.21 12.28 11.56 11.88 12.32 11.93 12.00 12.01 12.39 11.95 12.03 12.35 11.85 11.92 12.06 12.09 0 11.76 11.83 11.76 11.77 12.16 12.23 11.82 12.20 11.77 11.84 12.12 11.79 12.00 12.07 11.60 12.30 12.04 12.11 11.95 12.27 11.98 12.05 11.96 12.29 12.30 12.37 12.22 12.47 12.18 12.25 11.75 12.03 11.97 12.04 11.96 12.17 12.17 12.24 11.95 11.94 11.85 11.92 11.89 11.97 12.30 12.37 11.99 12.23 12.15 12.22 11.93 12.25 Managerial Report: 1) Compute the standard deviation for each of the four samples. Does the assumption of .21 for the population standard deviation appear reasonable? 2) Compute limits for the sample mean around u-12 such that, as long as a new sample mean is within those limits, the process will be considered to be operating satisfactorily. If sample mean exceeds the upper limit or if sample mean is below the lower limit, corrective action will be taken. These limits are referred to as upper and lower control limits for quality control purposes. 3) Discuss the implications of changing the level of significance to a larger value. What mistakes or error could increase if the level of significance in increased?
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