The Psychology of Quality and More

A Toolbook for Quality Improvement and Problem Solving (contents)

Variation

The Quality Toolbook > Variation

Understanding variation | Measuring variation| Measuring centering | Measuring spread

<-- Previous Chapter | Next Chapter -->

First section in this chapter -->

Variation is a major cause of quality problems and consequently many process improvement activities focus on identifying and reducing it. It is thus important to understand as much about variation as possible, even though its statistical nature can be disconcerting.

This chapter discusses the basic principles of variation, keeping the mathematical content to a minimum. In keeping with the style of the book, calculations are also minimized, consisting only of inserting numbers into simple formulae and using illustrated panels for calculations involving lists of numbers.

There are four main sections in this chapter:

• Understanding variation: Key principles of this important topic.

• Measuring variation: Principles of measurement of variation.

• Measuring centering: Mean, median and mode.

• Measuring spread: Range and standard deviation.