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Control chart for fraction defective

1. Collect data . number of items inspected ninumber of defective items riOrganize into subgroups. Example: . 2. Calculate fraction defective for each subgroup. 3. Calculate average fraction defective. . LCL is not applicable when <0. 4. Calculate the control limits. For example,.

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Control chart for fraction defective

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    1. Control chart for fraction defective Used for: Monitoring Rejection rate, Absenteeism, etc

    2. 1. Collect data number of items inspected ni number of defective items ri Organize into subgroups

    3. Example:

    4. 2. Calculate fraction defective for each subgroup

    5. 3. Calculate average fraction defective

    6. LCL is not applicable when <0 4. Calculate the control limits

    7. For example,

    8. 5. Check if all points within control limits? If YES, continue to use pbar for future data If NO, eliminate that data point and recalculate control limits

    9. 6. Draw the control chart. If LCL<0, let LCL=0 Note that control limits are constant if n is constant.

    11. 7. Examine for patterns Any run, trend, or non-random pattern could signal an assignable cause

    12. 8. Continue to use for future pbar can be kept constant, or pbar can be varied to include the next sample

    13. Variable sample size problem - alternatives Control Limits based on Average Sample Size Standardized Control Chart

    14. Service applications No of cheques with errors No of Purchase Orders with mistakes No of invoices not paid in time No of workers absent

    15. Conclusion: Control chart for fraction defectives can be used to monitor countable data

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