Summa Six
Sigma refers to the application of statistical
methods to problems beyond those normally covered in typical
courses dealing with Six Sigma. The techniques included fall
into the following areas:
(1) Multivariate
Capability Analysis  For products whose quality is
characterized by more than one measurement, assessment of
process capability with respect to each variable separately
can be very misleading. A multivariate capability analysis
determines the joint probability that all variables
will be simultaneously within spec. This requires use of a
distribution such as the multivariate normal distribution
which accounts for the covariances amongst the variables.
(2) Multivariate
Process Control Charts  Control charts based on
statistics such as Hotelling's TSquared are extremely
important in monitoring processes with multiple response
variables whose joint characteristics affect quality. When
combined with a dimensionality reduction procedure such as PCA (principal components analysis) or PLS (partial least
squares), such charts can be used to detect changes in a
process before they have a serious impact on the final
product.
(3) Capability Analysis and Control
Charts for NonNormal Data  Not all measurements are
normally distributed. When they are not, use of the normal
distribution for the estimation of capability indices and
the construction of control charts can be very misleading.
STATGRAPHICS Centurion adapts its capability analyses and
control charts to any
of 27 continuous distributions.
(4) Control Charts for Autocorrelated
Data  When a continuous process is sampled close
together in time, control charts must be modified to deal
with the autocorrelation. ARIMA control charts capture the
dynamics of a process and base signals on the residuals
after autocorrelation is removed. Cuscore control charts
are configured to detect specific outofcontrol patterns in
the presence of autocorrelation.
(5) Multivariate DOE
 Process optimization must take into account all of the
responses that characterize a product or service. The use of
multivariate desirability functions and optimization methods
is critical to overall success.
STATGRAPHICS Centurion
contains all of the procedures necessary to implement
Summa Six Sigma. For those interested in learning more
about the topics described above, a
twoday seminar is
offered.
