What does the 1.5 shift mean?

What does the "1.5σ shift" mean?

Without getting into a statistical and lengthy discussion on what the famous "shift" is, let us say that all processes produce variations over time. In the six sigma methodology (at least in the electronics industry), it was empirically validated that the shift of the distribution was about 1.5σ. This does not mean that with all processes, and in all industries, this shift is always within this 1.5σ. It does vary. For example, in the automotive industry we know, at least since 1980, that the shift is 1σ and not 1.5σ. Convention now has it that everyone follows the 1.5σ. One may simplify the interpretation of the shift as a drift of the process in the long term.