What is a process variation?
The process variation indicates how much a result differs from its target, where the objective is to find out what could cause this deviation. It is an important phrase in quality control management, especially in approaches like Six Sigma, since it influences directly either the consistency or quality of goods produced or services provided.
Types of Process Variation
- Common Cause Variation
The process itself entails a kind of variability that is brought about by the existing fluctuations. It is measurable and, in most cases, varies within three standard deviations from the mean value, thus implying a situation characterized as stable.
- Special Cause Variation
These unexpected factors cause variation and disturb the normal function of the process. Such cases are often easily seen and may greatly affect what is produced.
Short-Term Variation
Short-term variation, as it is more often referred to as within-group variation, signifies the natural fluctuations in a process for a relatively brief duration of time like days or weeks. The appearance of such variations can be attributed to the combined influence of insignificant and immeasurable small random elements.
Key Characteristics of Short-Term Variation
- Data collection is a short-term event that normally takes about 30-50 data points one after the other or immediately next to one another.
- It concentrates on random variations and does not address changes in the input of the process.
- It indicates the highest acceptable performance of the process due to the minimization of disturbing variables.
- This is used for comparing different processes on how well they can achieve certain objectives.
Long-Term Variation
Long-term variation is also known as overall variation and includes the changes in the output of a process over a lengthy period, usually months or years. This variation comprises both common cause variations and special cause variations, thus offering an all-inclusive perspective on the performance of a process under different circumstances.
Key Characteristics of Long-Term Variation
- Long-term variation relies on data gathered over a considerable period of time, which allows for attention to several factors such as material changes, operator variations, equipment shifts, as well as environmental conditions that affect the process.
- It is defined as a combination of within-group variation short-term variation and the variations that occur between groups, thus providing a more comprehensive view of how stable or capable any given process has been throughout its historical existence.
- In assessing long-term variation, one would ask, “Does my process ultimately meet specifications?” This evaluation takes into account the overall capability experienced by customers rather than just the expected potential ones.
Comparing Short-Term and Long-Term Variations
To understand the performance of Six Sigma and quality management processes, one needs to compare short-term variations with long-term variations. In this section, we will briefly explore key differences between the two and their implications.
Characteristics
Short-Term Variation
Time Frame: Data is gathered for a brief timeframe, most often days or weeks.
Nature: it shows a random difference among the segments, concentrating on the fundamental ability of the activity when outside issues are kept at low levels.
Measurement: This is indicated by the standard deviation for each subgroup, which in many cases is based upon the pooled standard deviation or average range of subgroups.
Key Question: “Does my new manufacturing sample meet its standards?”
Long-Term Variation
Time Frame: Information collection usually spans long periods of time, over several months or years.
Nature: It shows process consistency and capacity essence over time through both common cause variability and specific cause variations.
Measurement: This average standard deviation accounts for various differences in separate groups besides altering process inputs.
Key Question: “Do I comply with specifications throughout my process?”
Conclusion
Monitoring the quality is greatly influenced by short- and long-term change management. In this way, organizations can discover methods of improving and strengthening their processes and providing customers with superior products and services.
