The shape of your data, not just its average.
Chart guide
Improvement charts
Which chart answers which question, how to read each one, and when not to use it. Every page has a worked example from a service setting, and the numbers behind every chart.
Chapter 1
See variation over time
Is the process stable, getting better, or just noisy? These charts separate a real change from ordinary week to week variation.
Run chart
The simplest way to see whether something has changed.
Control chartsHow to read them, the rules, and which type to use.
I-MR chartOne measurement at a time, and how much it moves.
X-bar R chartAverages and ranges of small samples taken together.
p chartA proportion over time, such as the share of late cases.
c chartDefects counted in the same amount of work each time.
Chapter 2
Find the biggest cause
Where should the work start? These charts narrow a broad problem to the few causes that matter.
Chapter 3
See the shape of the data
Averages hide most of what matters. These show the spread, the tails and whether a process can meet its target.
Cp and Cpk: can the process meet what is asked of it?
Chapter 4
Compare groups, and see relationships
Is one team, site or shift really different, or does it only look that way? And does one thing move with another?
Several groups compared at a glance.
Whether two measures move together.
Chapter 5
Map a process
Before measuring a process, agree what it is. These put it on one page.
SIPOC
In preparation
Swimlane map
A process on one page: suppliers, inputs, steps, outputs, customers.
Value stream mapWhere the time goes, and how much of it is waiting.
Who does what, in what order.
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