Six sigma, originally invented by Motorola to improve its manufacturing process, aims to improve the process output quality through identification and removal of the causes of errors (defects) and reducing variability in business and manufacturing processes. A Six sigma level represents the reliability of the process. A higher six sigma level means a more reliable process and vice versa. For example, six sigma level one means that 61 percent of the parts produced by the process are defective while six sigma level six means only .00034 percent of the parts are defective. The calculation of six sigma level is based on number of defects per million opportunities (DPMO).
Things You'll Need
Gather the required information for calculating DPMO. Collect data for the number of units produced, the number of defect opportunities per unit and the number of defects.
Use the DPMO formula to calculate the number of defects in the process per million opportunities. The formula is given by:
DPMO=Number of Defects x 1,000,000 ((Number of Defect Opportunities/Unit) x Number of Units)
For example, consider a cell phone manufacturer who wants to calculate the six sigma level of its manufacturing process. For a given period, the manufacturer makes 83,934 cell phones. The manufacturer is required to perform eight checks to test the quality of its products. During testing phase, 3,432 of the cell phones were rejected.
Using the formula above, we get Defects= 3432 Opportunities= 83934 Defect Opportunities per unit= 8 DPMO=5111.158768
Use the six sigma table below to find out the level for respective DPMO value:
Six Sigma Level DPMO 1 690,000 2 308,000 3 66,800 4 6,210 5 320 6 3.4 For the example given above, DPMO of 5,111 is less than 6,210 and greater than 320. Hence, it results in a six sigma level four designation.