The customer service department is conducting a survey of the satisfaction level of those who call in for assistance. At the end of the call, customers are asked to rate the service on a 5 point scale, with 5 being the highest level of satisfaction. Anything less than a 5 is considered “defective” by the department. The company receives hundreds of calls per day.
The company has sampled seventy-five calls per day for the last eight days. The number defective in each sample is given in the table below. Calculate the UCL for a 3-standard deviation p-chart of the proportion defective.
Day | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
# defective | 17 | 15 | 9 | 3 | 20 | 10 | 12 | 14 |
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