AAOM Handbook

Measures / Analyse & Improve

Capability Histogram

The probability distribution of a measured or modelled result. It shows the relative frequency of occurrence for different results. The purpose of a Capability Histogram is to indicate how well a process can meet specifications over a nominated period of time. It provides a graphic of the variability that occurs in the result. The Capability Histogram also provides an easy way to identify the minimum, most likely (mode) and maximum values of the result.

Common Cause

Variation in process performance that regularly recurs – that is it is a ‘normal’ part of the process.

The tests commonly used to differentiate common and special cause variation are; • A point outside of the ±3σ values. • Seven points above or below the mean. • Seven points moving in the same direction. The probability of each of these events is similar, and is less than 1%.

Contributing Cause(s)

The items that are at the foundation (or root of) creating an issue identified by a measure.

Control Action

The activity taken in response to a validated contributing cause for an issue identified by a measure. The Control Action may be aimed at preventing the cause recurring (in the case of an undesirable issue), or at enduring that the cause is maintained (in the case of a desirable issue).

Control Chart

A chart that shows a measured result over time, and adds upper and lower control limits, plus a mean or centre line. Tests can be applied to the data to provide a quantitative, consistent and reliable indication of the stability of a process.

The purpose of a Control Chart is to indicate whether a process is behaving consistently over time.

© McAlear Management Consultants 2004

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