AAOM Handbook

MP.04 Define Purpose Measures Context

Purpose measures indicate the performance of the process by measuring output. The output performance of a process will always exhibit variation. Variation can arise from two types of cause – common causes and special causes. Common causes are defined as those that regularly recur when the process is behaving in a consistent way (this does not mean that the process is meeting specification – it might consistently not be meeting specification). The characteristics of consistent performance are that over time the average and the variation around that average are predictable. Special causes are defined as those instances where the process did not behave in a consistent way. Statistically, special causes account for less than 1% of the variation that occurs in a stable process. You can readily identify the common and special cause variation in performance using a control chart to present the measures of the process purpose and theory. Each special cause should be investigated as soon as it becomes evident in the Control Chart because it indicates that the process is probably changing (unstable) and hence may require an immediate intervention. Common causes do not need to be investigated in each instance. If the process is stable and meeting specifications, or if it is stable but not meeting specifications and you do not intend to take any immediate action (you have bigger fish to fry), then it is not necessary to collect the reasons for common causes. Importantly you only need to collect a representative sample of common causes, since in a stable process the same common causes will continually recur. Purpose To identify the output measures that reflect the purpose of the process. Quantity The purpose of a process shall be measured using the following parameters:  Effectiveness (output units on spec per time period (Time, Rate, Reliability & Quality)  Sustainability (process resourcing, asset condition and licence to operate)  Efficiency (Recovery, Unit Cost, ROI etc.) Quality Measurements of Purpose characteristics shall be reported to the following standards or, where a direct measure is not available, the most effective proxy(s) for the intended measure;  Effectiveness o On Spec Output Units per Time Period