This is the response to a question I was recently asked about how the DMPO to Process Sigma level is calculated and how practical is it ? Here is my voice of sanity in the confusion that surround the subject of DPMO and Process Sigma.
Just remember the following numbers and it will help to keep you straight:
Short Term Process Sigma of 6 is equivalent to 2 defects in a Billion Opportunities or Defects for a 2 tailed and centred process ( defects occur on both sides of the mean ). If it is a 1-tailed process and defects only occur on one side then it is only 1 defect per Billion needed to be called Process Sigma of 6.