Page 324 - Six Sigma Demystified

304 Six SigMa DemystifieD

Interpretation

The categorizations aid in our understanding of the types of factors that cause
variation in our processes. This categorization helps to reduce the number of
factors. At times, we can see the effects of interactions because they contribute
to one or more of the categories of variation.
It is important to understand that the multi-vari plot is not a control chart,
so it cannot be used to determine if there is a statistical instability in the
process.
In Figure F.21, the plot shows both the within-batch variation and the time-
to-time variation. Piece-to-piece variation (the variation between batches 1–5,
6–10, etc.) is negligible, but step changes to the process are clear between
batches 5 and 6, 10 and 11, 15 and 16, and so on.

Nominal group Technique

The nominal group technique (NGT) is a method of ranking subjective informa-
tion to build consensus. It is used to reduce a large number of ideas into a work-
able number of key ideas.

When to Use

The NGT can be used whenever consensus building is desired and there are no
data to otherwise narrow the list. It may be used as a precursor to data collec-
tion.

Define Stage
• To reduce a large number of potential projects into a workable number of
key projects

Analyze Stage

• To reach consensus on which solution, of a large number of potential solu-
tions, should be investigated in the initial stages of analysis
Methodology

Start by handing out a number of index cards to each team member. For fewer than
20 potential options, hand out four cards per member; for 20 to 35 five options, six
cards per member; and for more than 35 options, eight cards per member.