Situation Jack is a shift supervisor in a glass plant. He works on a process that makes thin-sheet glass used in small electronic devices such as computers and televisions. In this production process, one of the biggest problems is the waste of expensive glass material due to scoring defects. After the glass is formed, it is scored and cut into individual pieces. When a scoring defect occurs, two sheets of glass must be discarded. Jack, an engineer with some understanding of statistical tools, recently attended a class on statistical process control (SPC) applications for manufacturing processes. He has decided to use SPC techniques to study the waste from the scoring process. Available Data During a 4-week period, Jack kept data on the number of glass sheets produced per shift and the number of sheets that were defective as a result of the scoring process. He then computed the percent of defective sheets of glass for each shift. These data are given in the table entitled, “Percent of Defective Sheets of Glass.” Questions 1. How does the scoring process behave with respect to the percent of defective sheets? 2. What are some possible causes of the behavior you see? 3. What percentage of defective sheets of glass due to the scoring process can you predict for the future?
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