• One Sigma = 170 misspelled words per page in a book

• Two Sigma = 25 misspelled words per page in a book

• Three Sigma = 1.5 misspelled words per page in a book

• Four Sigma = 1 misspelled word in 300 pages• Five Sigma = 1 misspelled word in the Encyclopedia Britannica

• Six Sigma = 1 misspelled word in all the books in a city library

How good is good enough?

Yield PPM COPQ (COS)

99.9996549 % 3.4 < 10 %99.976 % 233 10 – 15 %

99.4 % 6,210 15 – 20 %93 % 66,807 20 – 30 %65 % 308,537 30 – 40 %50 % 500,000 > 40 %

How good is good enough?99% Acceptable Quality Levels

• For every 300,000 letters delivered.3,000 misdeliveris

• Out of every 500,000 computer restarts 5,000 crashed systems

• For 500 years of month-end closings 60 months would not balance

• For every week of TV broadcasting (per channel1.68 hours of dead air 1.8 seconds of dead air

How good is good enough?99% Acceptable Quality

Levels• At least 200,000 wrong drug prescriptions each year.

• Two short or long landings at major airports each day.

• 5,000 incorrect surgical procedures every week.

• 20,000 lost articles of mail per hour.

• No electricity for almost seven hours each month.

• 50 dropped newborn babies each day.

How good is good enough?How about 99.9% Acceptable Quality

Levels• Your heart would not beat for 8.8 hours per year • 15,000 newborn babies would be dropped on their heads each

year in hospitals• 500 Incorrect surgeries would be performed each week• 13,699 unsafe cans of soda would be consumed every day• A manufacturing process with 500 people would produce the

correct product 61% of the time

How good is good enough? OK then, isn’t 3 sigma better - Is 3

Sigma good enough?• US Postal service:

– 3 Sigma: 20,000 lost articles of mail/hour• Airplane Landings:

– 3 Sigma: 2 short/long landings every day• Drug prescriptions:

– 3 Sigma: 200,000 wrong drug prescriptions/year.• Unsafe drinking water almost 15 minutes each day.• No electricity for almost seven hours each month.• 5,000 incorrect surgical operations/week