Sigma Means Sum in Mathematics and Deviation in Industry
Sigma is the eighteenth letter of the Greek alphabet. It carries different technical meanings in different fields.
Sigma is the eighteenth letter of the Greek alphabet, written ฮฃ in capitals and ฯ in lower case. Its two technical lives run in parallel: the capital means summation in mathematics, so ฮฃ before an expression says add all these up; the lower case means standard deviation in statistics, which is why *six sigma* names a manufacturing standard demanding almost no defects. Greek also has a special final form, ฯ, used only at the end of a word.
- A Greek letter. *Sigma, ฮฃ.*
- Summation. *The sigma notation.*
- Standard deviation. *Two sigma.*
- Six Sigma โ a quality method. *Six Sigma.*
- Final sigma โ ฯ at word end. *Final sigma.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | sigma | Sigma. |
| Capital | ฮฃ | Summation. |
| Lower case | ฯ | Deviation. |
| Final | ฯ | Word end. |
| Method | Six Sigma | Six Sigma. |
- The sigma sign means add them all.Maths.
- Results within two sigma.Statistics.
- Six Sigma targets near-zero defects.Industry.
Greek letters used as symbols
- Sigma โ summation and standard deviation
- Pi โ the circle constant, and a product operator in capitals
- Delta โ change or difference
- Lambda โ wavelength, and functions in computing
- Mu โ the prefix micro, and the population mean
Greek *sigma*, the eighteenth letter, probably from a Phoenician letter name.
Why does sigma mean two different things?
The capital ฮฃ was adopted for summation and the lower case ฯ for standard deviation. The conventions grew up in different fields.
What is Six Sigma?
A quality management method aiming for so few defects that they fall six standard deviations from the mean.