Project Toolkitby Maxime Lab
Leadership and Business Skills · tool 2 of 11

Leadership and Business Skills · tool 2 of 11

Pareto Principle (80/20)

Pareto Principle (80/20): focuses effort on the few causes that produce most of the results.

Best for: Problem solving, prioritising · Time: 30 minutes with data
Domain: Across all domains · Focus area: Monitoring and Controlling

80% SpecEnvDataUIDocNetOther Defects by cause, sorted. The three blue causes produce about 80% of all defects: fix those first.

How it works

Roughly 80% of effects come from 20% of causes. A Pareto chart sorts causes from largest to smallest, with a cumulative-percentage line showing where the “vital few” end.

  • The ratio is a rule of thumb, not a law — 70/30 or 90/10 are common.
  • Requires data: counts of defects, delays, tickets, costs…
  • Works for personal productivity too: which few tasks create most value?

How to apply it

  1. Collect data on the problem (e.g. defects by cause, delays by reason).
  2. Sort the categories from largest to smallest and compute the cumulative %.
  3. Identify the categories that reach about 80% — the vital few.
  4. Focus your fixes there first, then measure again.
  5. Weekly: ask which 20% of your tasks will deliver 80% of this week’s goal.
In practice

Out of 120 bugs, 3 causes out of 10 produce 95 bugs. Fixing those three removes nearly 80% of the problem.

Pro tip

Don’t ignore the long tail forever — re-run the analysis after each fix; the ranking will change.

Quick check

Three causes out of ten produce 80% of the defects. Where do you start?

Sources

  • J. M. Juran, Juran’s Quality Handbook

Last reviewed 2026-11-02 against the PMBOK® Guide, 8th edition · Practitioner review pending · How this guide is made