The Lean Six Sigma Pocket Toolbook: A Quick Reference Guide to Nearly 100 Tools for Improving Quality and Speed

CHAPTER 7Variation Analysis

Purpose of these tools

• To separate special cause from common cause variation

• To detect trends and patterns in data that provide clues about the sources of variation (with the ultimate goal of reducing or eliminating those sources)

Deciding which tool to use

This section features two types of tools used to understand variation:

1) Time series charts, on which you plot data in the order of their occurrence

2) Capability calculations, which compare the range of actual process output against the range (specifications or tolerance) that meet customer requirements

When collecting process data, plot the data on one of the following charts before continuing with other analyses:

a) Time series plots (also called run charts ...