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ENGM 620 Fall 2010 Session Seven Homework Solutions Some of these questions do not have a universal answer. Therefore, the answers are written to elicit a range of potential answers based on differing perspectives. When this is true, it is particularly important for the student to concentrate on justifying their selected perspective. Chapter 11 (12) Discussion Questions 5. What are some applications of process charts in services? Could demerits (points off for mistakes) be charted? How? Process charts, as defined in the chapter, are tools for measuring quantifiable data. A process chart could be used to measure a quantifiable property of a service environment. This would include items that are time based or measurable such as response time, time spent to deliver a service or number of complaints. A demerit could be tracked if a predictable and standardized manner of assigning the demerits. This technique might contradict the approach to continued improvement. 6. What is random variation? Is it always uncontrollable? Random variation is that variation in a process that can be measured and analyzed. If it is controlled, then by definition, it is not random. A point that needs be made: The word “random” has a very specific meaning in statistics. Random variables are those values that are all members of the same set of variables and have an equal probability of occurring. Figure 12-1 demonstrates this property. 7. When would you choose an np chart over a p chart? An X chart over an x-bar chart? An s chart over an R chart? Charts are tools for portraying statistical information in an easy-to-comprehend manner. A p chart presents the proportion of defective parts whereas an np chart presents the number of non-conforming items. A p chart could be used to compare different items to observe the difference in the processes. An X chart is used to evaluate a population. An x¯ (x-bar) chart presents the same information for a sample. The cost and ease of getting an x¯ chart obviously make them preferable. An R chart presents the range of values; this is simply the high-value minus the low value. An s chart presents the range of standard deviations. The standard deviation presents the average variance that the sample points are from the mean or average value. An s chart shows much more detailed information whereas an R chart shows an overview of the situation Chapter 11 (12) Problems 5. Interpret the charts given in the book to determine if the processes are stable. Because of the way the data is presented in the textbook, some of the potential problems may be hard to see. a. Five successive points above the centerline: investigate for lack of stability b. Possible change in level (decrease): investigate for lack of stability c. Appears to be stable d. Seven points in a row steadily decreasing: investigate for lack of stability e. Large jumps (erratic behavior): investigate for lack of stability f. May be stable, possibly headed toward 15 points in a row within 1 sigma limits, which would need to be investigated.