Page 168 - The Handbook for Quality Management a Complete Guide to Operational Excellence

he successful quality system will address several aspects of process
and product control. Effective controls may be established only
Tafter understanding the fundamental nature of the variation to be
controlled.

Descriptive Statistics

Typically, descriptive statistics are computed to describe properties of
empirical distributions, that is, distributions of data from samples. There
are three areas of interest: the distribution’s location or central tendency,
its dispersion, and its shape. The analyst may also want some idea of the
magnitude of possible error in the statistical estimates. Table 9.1 describes
some of the more common descriptive statistical measures.
Figures 9.1 through 9.4 illustrate distributions with different descrip-
tive statistics.
Many readers may be familiar with these statistics from their college
curriculum. They are used in defining confidence intervals and to accept
or reject statistical tests via hypothesis testing. These tests are somewhat
dependent on the specific distribution of the population from which the
samples are taken.

Enumerative and Analytic Studies
Deming (1975) defines enumerative and analytic studies as follows:

Enumerative study. A study in which action will be taken on the
universe.
Analytic study. A study in which action will be taken on a process to
improve performance in the future.

The term universe is somewhat synonymous with population: the entire
group of interest. For example, the expected voters in a specific election
might constitute a population of interest.

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