Voice of Customer against Voice of Process
VOC generally means the Voice of Customer. It is a representation of Customer’s requirements and is expressed as targets or Specification limits. These limits can exist both on the lower side and upper side and are an indication of what the customer perceives to be acceptable and is willing to pay for.
The Y in a Six Sigma project is generally taken as a Voice of Customer, having both the upper limits and lower limits. The data values lying within these limits are considered to be acceptable and those lying outside (both on the upper side and lower side) are considered to be defects.
Voice of Process is the performance of a process over a period of time. The upper and lower limits can be plotted on the Process Performance graph showing the gap between the Voice of Customer and the Voice of Process. If the VOP is lying within the VOC, then everything is fine with the process. But if VOP is lying outside the VOC, then it means that the process is generating defects and an improvement project has to be undertaken.
Let us understand this with the help of following figure:
- The area under the Blue curve (blue line) represents the overall Variation in the process and is called as Voice of Process.
- The area under the Upper Limit and Lower Limit (green line) is the Acceptable variation in the process and is also known as Voice of Customer. This variation is also known as Common cause variation.
- The area outside the green line and within blue line(below green line) and displayed as purple filed area is the defects that are present in the process.
- This purple painted area in the process is the Special cause Variation which is negatively affecting the process performance and has to be eliminated to bring the process under control.
- Hence, this gap between the Voice of Process and the Voice of Customer is the improvement area for which the Six Sigma project should be initiated to bring the process under control.
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