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Training and Learning 289
Performance

Time
Screening Breakaway Marginal Characterization Optimization Tracking
procedures moves analysis studies applications routines

Information analysis ‘Parameter Mathematical modeling
design’
Figure 18.9 Choice of statistical tools along the learning curve.

methods, as already pointed out, offer a prescribed set of techniques, whereas statisti-
cians represented by Box encourage `a la carte selections used according to the progress
of investigation: screening, characterization or optimization. Thus the actual design
of an experiment is shaped by the existing knowledge about the subject of study, and
the size of experiment is defined according to the expectation on the quality of the
resulting information (e.g. level of resolution of parameter effects). In this respect the
Box approach is much more versatile and flexible, as it offers opportunities for quick
screening of a large number of parameters, followed by detailed mathematical model-
ing of the critical ones that remain or, in some cases, a quick breakaway from current
ranges of parameter values for better results, culminating in a final fine-tuning of
parameter settings for optimized performance. Indeed on-line optimality seeking (by
response surface methodology) and tracking (by evolutionary operation) are strate-
gies that are sorely absent from Taguchi methods; no statistical quality engineering
training or application would be complete without their inclusion. Figure 18.9 shows
the sequence of major tools to be applied as performance progresses along the learning
curve.

18.7.3 Directions
In discussing the technicalities of statistical quality engineering with management
and operations personnel, measures should be taken to ensure that they do not fail
to see the forest for the trees. Hence, it would be useful to explain the historical
background of the various schools of thought that exist in the profession today. An
awareness should be brought about of the richness of experimental design literature,
scope of applications, and practical conditions to be encountered in practice, 60,61 and