SC QUALITY GUILDPareto builder
SCQUALITYGUILD.COM/CALCULATORS/PARETO-CHART.HTML
Sorts, cumulates and draws the 80 percent line, then tells you whether there is really a vital few or whether the categories need re-cutting.
SORTS, CUMULATES, AND TESTS FOR A VITAL FEW · FREE · NOTHING YOU TYPE LEAVES YOUR BROWSER
Q-BotClick for an explanation of this calculator.Pareto builder
SORTS, CUMULATES, AND TESTS FOR A VITAL FEW| CATEGORY | COUNT | SHARE | CUMULATIVE |
|---|
For educational use. This page is a study aid. The method behind it has far more depth and detail than one page and one tool can cover, and what you see here is not everything the method offers or everything this site offers. For full understanding and application, use the governing standards and texts, and seek further education, training or qualified advice. Results depend on the data you enter, so check them before relying on them.
What the 80 percent line is and is not
A Pareto chart sorts categories by size and draws a cumulative curve across them. The convention is to mark where the curve crosses eighty percent, and to call whatever sits to the left of that mark the vital few.
There is no law that says eighty percent of your defects come from twenty percent of your causes. That is an observation that is often true, not a rule that must be. Plenty of real processes produce a flat Pareto, and a flat Pareto is information — it says the problem is general, not concentrated, and that hunting for a single big cause will waste your time.
The chart depends entirely on how you cut the categories
This is the part that gets skipped. Here are the same one hundred defects, from the same plant in the same week, categorized two different ways:
| Cut by operation | Count | Cut by failure mode | Count |
|---|---|---|---|
| Op 30 | 18 | Seal nick on assembly | 52 |
| Op 10 | 17 | Burr at cross-drill | 24 |
| Op 40 | 17 | Paint run | 9 |
| Op 20 | 16 | Label misaligned | 8 |
| Op 50 | 16 | Packaging damage | 7 |
| Op 60 | 16 | — | — |
Cut by operation, you need five of six categories to reach eighty percent. The chart is flat. It says there is no vital few and everything is equally bad.
Cut by failure mode, one category is fifty-two percent on its own and three of five get you to eighty. The chart says: go and fix the seal nick.
Same defects. Same plant. Same week. One chart sends you away empty-handed and the other hands you the job. If the first cut looks flat, re-cut it before concluding there is nothing there.
Count what it costs, not just how often
A Pareto by occurrence treats a scratched label and a field return as one each. Weighting the same categories by cost — scrap value, warranty, hours of containment — routinely reorders the chart completely, and the cost chart is usually the one worth acting on.
Run both. Where they disagree is where the interesting conversation is.
Where Pareto charts go wrong
- "Other" is the biggest bar. If the catch-all category makes the top three, the categories are wrong and the chart cannot be read.
- Unlike units added together. Counting defects, returns and complaints in one chart means the tallest bar belongs to whichever is easiest to record.
- One period treated as the truth. A single month's chart is a sample. Check that the top category is still the top category over several before committing resource to it.
- It is used to close the analysis rather than open it. Pareto tells you where to go looking. It does not tell you the cause, and the biggest bar is not a root cause.