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Control chart for fraction defective

Control chart for fraction defective. Used for: Monitoring Rejection rate, Absenteeism, etc. 1. Collect data. number of items inspected n i number of defective items r i Organize into subgroups. Example:. 2. Calculate fraction defective for each subgroup.

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

  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.

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

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

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

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

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

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