Tools › Quality › Improvement › Pareto and Root Cause › Example
Montgomery Figure 5.17: Pareto chart of the tank defect data
| Tool | Pareto and Root Cause |
| Source | Montgomery, D. C. (2013). Introduction to Statistical Quality Control, 7th ed. Wiley, Hoboken, NJ. Section 5.4, Figure 5.17. |
| Level | Undergraduate |
Problem
Final inspection of aircraft tanks recorded 166 defects in 19 categories. Rank the categories, draw the Pareto chart with the cumulative percentage line, and identify the vital few that account for about 80 % of the defects.
Inputs to Enter
- Tallied counts (loaded by default): Incorrect dimensions 36, Parts damaged 34, Machining problems 29, Masking insufficient 17, Supplied parts rusted 13, Adhesive failure 6, Film on parts 5, Processing out of order 4, Salt-spray failure 4
- Wrong part issued 3, Unfinished fairing 3, Misaligned weld 2, Paint out of limits 2, Voids in casting 2, Delaminated composite 2, Powdery alodine 1, Paint damaged by etching 1, Primer cans damaged 1, Improper test procedure 1
- Weighting by count, vital-few cut at 80 %
Answers
- Total 166 defects in 19 categories; rank 1 Incorrect dimensions 36 (21.69 %)
- Cumulative share after the first three categories 99/166 = 59.64 % ("about 60 %" of the total, as the book notes); after five 77.71 %
- Vital few at the 80 % cut: six categories carrying 135/166 = 81.33 %
Notes
The tool's default inputs are this example; press Submit to reproduce it. The counts are as reproduced in the IMSL chart programmer's guide, which cites Montgomery's figure; the 5-Whys chains loaded with the example are illustrative, not from the book.