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Stages in Statistical Applications 269
Quality
Management

Quality Quality
Technology Information

Figure 18.1 Important dimensions of quality improvement initiatives.

to be generated. The full quality and productivity potential of an organization can be
realized, however, only with the presence of a third dimension, namely a quality infor-
mation capability. Quality information know-how is statistical in nature; it is essential
for intelligent decision making based on data collected from the performance of pro-
cesses or products in the face of natural variabilities. Statistical quality control (SQC) 25
is an established area of study dedicated to this requirement; as will be discussed in
the next section, there is now a wider scope of application of statistical techniques for
quality improvement beyond traditional SQC. Generally, only an effective interplay
of management, technology, and information can bring about balanced and sustained
advances in quality levels, as depicted in Figure 18.1.

18.3 STAGES IN STATISTICAL APPLICATIONS

In chronological terms, the adoption of statistical techniques in manufacturing in-
dustries has progressed in three broad stages. The first is product inspection, where
statistical sampling plans help determine the product sample size and decision rules
(e.g. the acceptance number). Sampling inspection is, strictly speaking, not a qual-
ity improvement tool; all it does is attempt to detect products not conforming to
requirements during inspection, the effectiveness of the attempt being reflected by
operating characteristic (OC) curves of sampling plans. Its futility is expressed in the
oft-repeated saying: ‘Quality cannot be inspected into the product’.
At the next stage, attention is turned ‘upstream’, that is, to the process that generates
the product in question, leading to techniques such as process capability studies and
process control chart applications. The effectiveness of statistical process control (SPC)
lies in its ability to prevent the generation of unsatisfactory products; however, as
in acceptance sampling, this is basically a negative and passive approach, since no