CTx (Critical to x) Requirements

Six Sigma’s role is to help organizations produce maximum value while making the most efficient use of resources. Six Sigma utilizes projects – defined systems that operate for a finite period and use prescribed processes to achieve a preplanned goal or purpose. What the project must accomplish and how well it must perform is determined by the allocation of requirements. A requirement is a necessary attribute of a system – a statement that captures a capability or characteristic that a system must possess in order to have value.

  1. Customer requirements are derived from the needs and desires of the external customer – the purchaser or end user of the project’s output. The needs of external customers are most often expressed in qualifiable terms, and customer objectives usually indicate what features they would like in terms of either the quality or the purpose of the output.
  2. Business requirements are the essential activities of an organization. They deal mainly with input and are derived from the needs or constraints established by internal customers – individuals or functional departments within the organization. These requirements may also be indirectly influenced by the constraints placed on the business by government or regulatory bodies.

All requirements are not equal in importance – the most important ones are referred to as CTx, or critical to x, requirements. CTx requirements help Six Sigma team members to analyze and prioritize their time and energy in an efficient and effective manner. All requirements are important, but CTx helps prioritize them to deliver the greatest benefits.

Requirements are more than just writing down what stakeholders want. CTx requirements have particular and defining characteristics:
  1. CTx requirements relate to business or customer requirements – Gathering requirements is necessary to ensure processes are designed to meet those requirements. A Six Sigma team translates those requirements into a measurable form while retaining the original intent. Once requirements are defined and refined, the CTxs can be used to create specific objectives.
  2. CTx requirements are measurable – If CTx requirements are to be useful, they must be measurable. This is so the Six Sigma project team can accurately determine whether the provided solution satisfies the requirement. As a requirement goes through various operational levels, it transforms from customer statement to functional analysis to measurable characteristic.
  3. CTx requirements are identifiable at different levels of operation – Through the various stages of refinement, the wording of the CTx requirement changes (less abstract, more specific). The property of the requirement must be clear at each stage and throughout the project life cycle. The team must be able to identify requirements so it can prioritize project resources.
  4. a change in CTx requirements can impact the system – A requirement has a number of types of relationships within a project. Each one impacts the project in different ways and with varying degrees of severity. As requirements emerge and are refined, the Six Sigma team needs to analyze the consequences of any change in relation to system factors.
CTx classification and analysis

Once a Six Sigma team know what’s important to the customer, it can translate needs into CTx requirements. The team must establish the capability to achieve these goals in an effective and efficient manner. Six Sigma projects address three main areas of improvement – schedule (“on time”), quality (“on spec”), and cost (“on budget”). With CTx requirements, establishing the aspect of the requirement (represented by x) is crucial, in order to address the appropriate area(s) of improvement.

Each type of CTx requirement has an important function in a project:
  1. Critical to quality (CTQ) requirements – the most common of all “critical to” requirements – deal with the fitness of the output to fulfill customers’ expectations from a product or a service.
  2. Critical to cost (CTC) requirements must be met in order to keep the costs related to the process within budget.
  3. Critical to process (CTP) requirements must be met in order to control the relevant process and support the validity of measurements.
  4. Critical to safety (CTS) requirements must be met in order to produce a product or service that is safe for customers’ use, and is safe for employees to produce and deliver.
  5. Critical to delivery (CTD) requirements must be met in order to ensure an appropriate and timely delivery of output to customers.
CTx requirements are distilled from
  • The voice of the business (VOB) is the term used to describe the process for capturing business requirements – the needs or constraints of internal customers. The VOB is mainly concerned with efficiency, productivity, and internal quality. It comes from both internal and external analyses of the industry and competition, and from the regulatory, economic, and legal environment. The VOB is most directly influenced by the necessity of solving operational problems and improvement issues.
  • The voice of the customer (VOC) is the term used to describe the process for capturing customer requirements – the needs or desires of external customers. In modern business, the VOC has evolved from a mere performance assessment to a roadmap for organizational process improvement – most CTx requirements stem from the VOC. Data gathered from the VOC helps an organization decide which products and services to offer, and where to focus quality improvement efforts.

Making sure customer needs and wants are captured and communicated in a systematic manner is important. If a customer isn’t satisfied with the product or service, she will not buy it. Whether CTx requirements stem from the voice of the customer or the voice of the business, their purpose is the same – to create value. This means finding a balance between efficiency and effectiveness. Six Sigma team members must take all cost and revenue implications into account. They must realize that project failure isn’t due solely to production defects but also to marketing and sales defects that incorrectly interpret customer expectations. After being prioritized, VOC and VOB requirements need to be quickly translated into specific functional requirements. Requirements analysis starts with customer and business requirements and travels through successive levels of details at the system, subsystem, and component levels, ending with specific measurable tasks, activities, or specifications.

In Six Sigma, requirements that are critical to success are referred to as critical to x (CTx) requirements. Six Sigma translates customer needs and desires into CTx requirements, and then links these requirements to measurable organizational processes. The characteristics of CTx requirements are that they are measurable, they are identifiable at every level of operation, they relate to business or customer requirements, and a change in requirements can impact the system.

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