Question 2(20%) Which type of control chart (p, np, c, u) is most appropriate to

Question

Question 2(20%)

Which type of control chart (p, np, c, u) is most appropriate to monitor the following situations, and why?

i) The number of thefts in a city over a period of time. (4 marks)

ii) Theperformanceofthebrakingmechanismofacertainmodelofautomobile.The

car is expected to stop within a certain distance. (4 marks)

iii) The number of typographical errors per page will be controlled. Data is randomly chosen and obtained daily on the number of errors in 30 pages. (4 marks)

iv) The proportion of customers that are satisfied with the operation of the local

housing authority. (4 marks)

v) The number of potholes in highways (4 marks)

Explanation / Answer

i) The number of thefts in a city over a period of time - np chart

ii) Theperformanceofthebrakingmechanismofacertainmodelofautomobile.The car is expected to stop within a certain distance - c chart

iii) The number of typographical errors per page will be controlled. Data is randomly chosen and obtained daily on the number of errors in 30 pages - u chart

iv) The proportion of customers that are satisfied with the operation of the local housing authority - p chart

v) The number of potholes in highways - np chart

p charts

For discrete attribute data, use the p chart.

np charts

The np chart follows the same principle as the p chart, but actually plots the number of instances in a category over time rather than the proportion in the category.

c charts

The c chart is similar to the np chart, in that it requires equal sample sizes for each data point.

u charts

The u chart is a more general version of the c chart for use when the data points do not come from equal-sized samples.

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