Voice of the Process (VOP) In Six Sigma

The Voice of the Process (VOP) in six sigma is the way the process communicates performance in relation to customer expectations and needs. These communications take place via process metrics, which are indicators of the current state of the process. To establish a baseline, it is important to know how the current state operates before you attempt any changes or improvements. It is crucial not to alter a process without understanding the current performance or variation.

Standard Deviation and Mean

The standard deviation and mean are the most used statistical measures for a process. After these measures are calculated, it is possible to conduct a capability study. A capability study is a measurement of the standard deviation between the process average (in sigma units) and the closest spec limit. A process’s standard deviation will increase as the average moves from the middle of tolerance. In other words, there will be fewer standard deviations between the average and nearest specification limit. The probability of items not being specified increases when they are close to the limits.

Each stable process has a predictable range for performance. Stable processes are those that are under statistical control. This means that special causes have been eliminated. Performance is only affected by normal operations. Performance measures are determined by the mean of outcome values that reflect the customer’s expectations.

For the most critical processes, organizations must have a reliable way to gather timely and consistent data. These processes must satisfy both the internal and external customers requirements in order to survive.

Capability Indicators

Voice Of The Process
Capability Indicators

Two of the most common indices used to determine whether a process can satisfy its customers are:

  • Cp, which is used to measure variation or whether data falls within specified limits (USL, LSL). This is often referred to as process potential. It is the measure of how wide the process distribution is relative to a set limit. 
  • Cpk measures how close a process comes to meeting its specs and how well the data fits within those limits. It indicates the process’s ability to produce products according to specs. 

(Voice Of The Process in Six Sigma) Are the Specs Accurate?

These process capability indices can only be used if the specs are accurate. Process capability is a function of the specs. Processes that are under statistical control, and otherwise distributed, can be considered capable. The process capability indices are used to measure the “natural variability” that a process experiences relative to its specification limits. This allows for different processes to be compared in terms of how well an organization controls them.

The greater the Cpk, the more stable a process is and the less likely that any item will be outside of the specification. Cp for a process lies in the range of 1.33 to 2.0. A process is considered not capable if it has a Cpk below 1.0. However, if the value is greater than 1.0 it is considered to be capable. Cpk values should be between 1.33 (minimal acceptable industry level to satisfy customers), and 2.0 for six-sigma processes. 

(Voice Of The Process in Six Sigma) Determine What the Customer Will Take

Here’s an example: A study was done on the wait time at a hospital for service over a period of four weeks. Data collected to conduct a process capability study shows how the process is centered as well as its variability. According to the clinic study, the average wait time for the service was 8 minutes. The standard deviation was 1 minute.

What is the process’ ability to meet customer expectations? This is a difficult question for most companies to answer. We don’t know the customer’s tolerance for waiting longer than necessary to receive a service. While organizations can spend a lot trying to reduce wait times to zero, it may not be what the customer is expecting.

Voice Of The Process – How well does the organization meet customer expectations?

The true question for an organization is: How well does it meet customer expectations? Because they don’t know their customers’ expectations, this is a difficult question for service providers to answer.

Many processes in the public and private sectors, including healthcare, do not require customers to specify their requirements. Acceptable limits must be established for processes that do not have customer specs. Tolerable variations must be identified by actual customers of the process. The authors suggest developing an Upper Toleration Limit and Lower Toleration Limit to allow for either Run Charts, or Control Charts. These Lower Toleration Limits (UTL and LTL) will replace the Upper and Lower Control Limits in order to calculate Cp and Cpk.

A customer may be asked a question like: “How long do you want to wait to see a doctor for a flu shot?”

Many customers know that waiting times are inevitable. Therefore, it is important to get an average of wait time from several customers. While everyone would prefer to have no wait time, most people are willing to accept a minimum wait. It is important to define the minimum acceptable wait as the Lower Specification Limit. It is possible to spend a lot of time trying to reduce wait times to zero. This may not be what the customer expects. Our limited resources should be used to improve our processes and meet customer expectations.

What is the Voice of the Process (VOP)?
What is the Voice of the Process (VOP)?

The Voice of the Customer (VOC)

We must first obtain the Voice of the Customer (VOC), in order to understand the expectations of our customers when they receive a service from us. This allows us to compare the output of the process with the customer’s expectations. It is difficult to obtain the VOC. This requires considerable diligence. It is important to understand who our customers are before you can separate them into different categories, such as:

  • Internal Customer
  • External Customer

Once we understand our customers

Once we have an understanding of our customers, we can develop a method to get the VOC. This is not an easy task. It is essential to develop a method that can continuously track and record our customers’ wants and needs and alert us of any changes. Surveys, telephone interviews or questionnaires administered in person are some of the methods used by organizations. Some market firms use surveys to get feedback from their customers. A company’s existence is dependent on customers satisfaction. 

We need to understand the requirements of our customers, regardless of how we obtain the VOC.

  • What does the customer need?
  • What does the customer want?
  • What are the customers “Satisfier”?
  • What are the customers “Dis-satisfiers”?
  • What are the customers Future requirements?
  • What does the customer expect?

It is important to decide in advance the level of detail required for each potential VOC category. Customer’s needs change over time. It is important to have a process of regular monitoring to spot these shifts.


Voice of the Process (VOP) and Voice of the Customer (VOC) must be integrated by organizations to ensure that processes are reliable and can meet quality and cost requirements. VOP indicates how well a process can meet customer needs. We must monitor the expectations and needs of customers in order to ensure that our processes are meeting their requirements.

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