CTQ | Lean Six Sigma, Six Sigma Certification

Any aspirant preparing for Lean Six Sigma Certification Exams of ASQ or IASSC, it is important for you to understand the difference between CTQ, Primary Metric and Secondary Metric.
In Lean Six Sigma, the term CTQ is very commonly used. CTQ is an acronym Critical to Quality. As the name suggests, any attribute, parameter, factor or metric that is critical to the quality of the product or service you are offering to your customers can be considered as CTQ.
One important element of CTQ is that it should be measurable, directly or indirectly. As we all know, anything that cannot be measured, cannot be achieved. More or less, it is difficult to maintain the desired level of quality for any product or service, if an important or critical attribute is not measured.

In the context of improvement projects in Lean Six Sigma, using the framework of DMAIC, the objective of such projects will be for Lean Six Sigma Green Belt or Lean SIx Sigma Black Belt will be to improve a given CTQ. For example, if on time delivery could be a CTQ for the business because the customer wants your products or service on-time. Thus CTQ emanates from the customer. There are usually many CTQs for any product or service. But the DMAIC Project will have to focus on improving only CTQ at a time. Especially the one which is not performing up to the mark, as desired by customers. This becomes the primary metric of the project. In this example, On-time delivery could be a Primary Metric. The purpose of the project will now be fully aligned to improve this primary metric.
If that is the primary metric, the question we need to answer is what is a secondary metric in a Lean Six Sigma Improvement project? To understand how to identify secondary metric, we will take a step back and talk about the purpose of improvements in using Lean Six Sigma or any other structured problem solving approach.

Purpose of Using Structured Framework like Lean Six Sigma DMAIC for Problem Solving

There are many benefits of using such a framework, but come to the most pertinent point. Any improvement that is brought about by compromising or reducing the performance of any aspect of the business, product or service is not real improvement. It is mere optimization and doesn’t need problem solving skills. For example, if one adds more employees, equipment or cost to reduce the on-time delivery, that isn’t true improvement.

Hence we will need to ensure that Cost of Servicing and Quality of Service does not deteriorate as we try to improve On-time delivery.
These become Secondary Metrics for the project. Thus Secondary Metrics are those parameters or CTQs that will be monitored and sustained at current level, as we try to improve the primary metric. Secondary Metrics are also called Consequential Measures or Counter-measures.

While any DMAIC project should ideally have only one Primary Metric, it can have as many secondary metrics. All secondary metrics will be monitored and throughout the project, care will be taken to ensure there are no side effects on the Secondary Metrics as a result of any improvement in Primary metric.

The best way to identify secondary metrics will be through brainstorming. An alternate way would be to look for statistical relationships between various CTQs.


Some of the major attributes of CTQ include:

  • A single meaning for each metric across all geographic locations.
  • Defining the process owners who are responsible for tracking the CTQ.
  • Clearly defined defects and opportunities in the process.
  • A consistent measurement system to provide accurate and precise measurements.
  • And, it must be derived from the VOC so that it provides a strong linkage to the VOC.



The voice of the customer (VOC) is gathered and converted into technical requirements in this phase. A business case is then established and a project charter is prepared along with milestones. A team is also formed to carry out the project. Roles and responsibilities of the team members are also set during this phase. These activities are accomplished using tools such as Quality Function Deployment (QFD); Failure Modes and Effects Analysis (FMEA); the Suppliers, Inputs, Process, Outputs, and Customers (SIPOC) diagram; the Integrated Product Delivery System (IDPS); target costing; and benchmarking.


In this phase, the concept design is developed by formulating alternative concepts and choosing the best concept after evaluating the alternatives. Risks associated with the chosen concept design are also determined. The functional requirements and their Critical to Quality (CTQ) attributes are identified by the Six Sigma team. The CTQ attributes are deployed after assessing their effect on functional requirements. Raw materials and their procurement plan with the related manufacturing plan are created during this phase. In addition, the Sigma capability is predicted. These activities are accomplished using tools such as smart simple design, risk assessment, FMEA, engineering analysis, materials selection software, simulation, DOE, systems engineering, and the capability of the process is evaluated to verify if the CTQs can be met.


The design is optimized for reliability and performance by developing detailed design elements. This helps optimize the Sigma capability and cost. These activities are accomplished through manufacturing database and flowback tools, a design for manufacturability, process capability models, a robust design, Monte Carlo methods, tolerancing, and Six Sigma tools.


The prototype is tested using formal tools to validate the design. After evaluating the performance, failure modes, and risks of the design, new requirements to be met are sent to manufacturing and sourcing units. The design is iterated until it meets the requirements of the customer. A final phase review to assess the reliability is also carried out to validate the design. The term Verify is also used interchangeably for this phase. These activities are accomplished through accelerated testing, reliability engineering, FMEA, and disciplined New Product Introduction (NPI).


In a recent Lean Six Sigma Project kick-off meeting of one of my clients, after the teams presented their project charters, the business leader made an extempore announcement that the best and most successful Lean Six Sigma project will receive a special recognition and the team members will be lucratively rewarded.
Immediately few of them wanted to know what criteria will be used for selection. The business leader indicated that I will be one who will define the criteria for successful Lean Six Sigma Project.
Factors that I consider among the criteria for success of Lean Six Sigma Projects are arranged in the descending order of their importance in the below list:
Project Scope – Lean Six Sigma projects without well-defined scope are bound to fail, but they end up creating a lot of mess around. Scope usually refers to the boundaries of any project. A poorly defined project is one which hasn’t balanced the Project Goal, Scope and Timelines. Also, poorly communicated scope and not defining what is out of scope are equally important.
Retains interest and commitment of the resources – Improvement projects are successful when its team members contribute their best. Lean Six Sigma projects usually challenge the existing paradigm. Hence without the wholehearted and continued participation of the team members, no project will be successful. The sponsor/champion and the Green Belt/Black Belt are entrusted to retain the interest and commitment of the resources.
Attracts adequate buy-in from key stakeholders – Stakeholders of any project could either be the decision makers, important players who influence the decisions or even impacted parties. Successful Lean Six Sigma projects will have to manage the expectations of all the above stakeholders from time to time and create adequate buy-in. Rather than focusing too much on technical root cause analysis, the emphasis should be on how Lean Six Sigma project can bring about mid-to-large change in the organization.
Flawless execution– Immaterial of the breadth and depth of the analysis done in any Lean Six Sigma project, what sticks out is execution. Well led and implemented the project is bound to be successful, as even the quality of data collected and analysis is a function of the flawless execution. Adherence to weekly team meetings, project milestones, and tollgates reviews are some simple and easy signs to evaluate execution. Further unbiased data collection and analysis, open minded assessment of solutions, in-depth piloting and sustained monitoring are additional measures of flawless execution.
Identifiable impact on customers– As the proof of the pudding is in the eating, so is the success of any Lean Six Sigma in positive impact it creates on customers. Usually, organizations evaluate the success of projects based on the performance of the CTQ (before-after studies). While this is definitely a good way to assess the impact, more often than not such movements in CTQs aren’t felt by customers. Considering several other business parameters to validate the impact of the CTQ, including post improvement Voice of Customer may be a very good method. For example, a reduction in defects certainly will reduce the rework effort, increase productivity, reduce complaints, apart from increasing customer satisfaction.
Making a discovery – Any successful Lean Six Sigma project should unearth something new, make a discovery about the problem. A project without a discovery could mean we are fixing obvious things. In order to ensure the project team makes a discovery, the quality of work done in the Measure and Analyze phase have to be evaluated. Have the teams identified all possible causes to the problem? Have they collected data of good quality and quantity? Have they holistically analyzed the data to make the discovery? And finally what is the discovery?
Based on my experience with Lean Six Sigma in the last 2 decades, I would consider these 6 factors as significant elements of the successful project.


Analyze Phase of Lean Six Sigma Project is the third phase. Following are the deliverable of this phase that Six Sigma Green Belt should deliver with her team:

Statistically Validate Root Causes

The data that has been collected in the Measure Phase is used to draw statistical associations between CTQ measures and causes. The causes that are statistically significant are the root causes. There are a variety of statistical tools to establish this association. Depending on the type of data – continuous or discrete – tools are selected. Such tests are generally called as Hypothesis tests. 2-t Test, Z-test, t-test, ANOVA, Chi-Square Test, Correlation, Regression, etc., are few common hypothesis tests.
The procedure to perform, and interpret all the above tests are usually covered in detail in Lean Six Sigma Green Belt Training programs.

Perform Value Stream Mapping & Process Value Analysis

Value Stream Mapping (VSM) is a popular tool used in Lean methodology; as an alternate approach to statistically identifying Root Causes, or in conjunction with it is the application of Value Stream Mapping and Process Value Analysis. It is used to identify the 7 types of Wastes (Muda – in Japanese) in a process. VSM is a holistic method to visually document the way in which value is getting built in a process.
The 7 types of process wastes are generally referred to as Non-Value Added tasks in conventional Six Sigma. The procedure of associating every task in a process as either Value Adding (VA), Non-Value Adding (NVA), or Value-Enabling (VE) is called as Process Value Analysis.
These methods are very useful in projects where extensive data collection is not possible, or in projects with Turn-Around Time or Delay reduction.

Control-Impact Matrix

The final deliverable of the Analyze phase is to summarize all the findings from Statistical validation or Process Value Analysis (& VSM) in a 2×2 matrix called as Control-Impact Matrix. It is important to ensure that the project doesn’t end up as an academic exercise or research study. Hence, the Lean Six Sigma team needs to identify root causes which have high impact, and well within the control of the team. This is done through a team discussion with the involvement of the project sponsor.
Once the root causes have been identified, & a formal Analyze Tollgate review is completed; the Lean Six Sigma Project is ready to move to the Improve Phase. Next >>>


Control phase is the fifth and final phase of Lean Six Sigma projects. Following are the deliverable of this phase:

Prepare Control Plan

Control Plan or Process Management Plan is a document ensuring that a robust mechanism to monitor and follow-up is established before the solution is implemented. Most Lean Six Sigma projects don’t exist after a few years of implementation. Usually, it is because of a poor control plan. A control plan covers: which metrics will be monitored, method of monitoring, how often, by whom and what has to be done when they go out of control (aka Reaction Plan).

It is recommended to have a control plan that is easy to implement and sustain.

Final Implementation

Real implementation of a solution is part of the Control phase. Change management skills of the green belt is tested during this stage.

Establish Statistical Process Control

As a part of the control plan, the method of monitoring has to be specific. Statistical Process Control uses well known Control Charts or Shewhart Charts. A control chart, computes the lower and upper control limits as a threshold to monitor any process measures; like CTQ. As the threshold is breached, the reaction plan has to be triggered. As the name suggests, it is a chart that is based on the principles of statistics, and hence there are no false alarms. Instilling the discipline of creating control charts and monitoring as per Control Plan is part of the rigor of a Lean Six Sigma Green Belt.

Benefits Computation & Closure

The last deliverable of the Lean Six Sigma project is Benefits Computation and Closure. But before that, the project is monitored for enough time (2 weeks to 2 months) to ensure that benefits are sustained. When the Lean Six Sigma Team is satisfied with the results, then the improved process is formally handed-over to the process owner.

Financial and non-financial benefits are computed based on actual results, and a formal sign-off from the finance manager and sponsor is obtained. This will be the project closure.
The Lean Six Sigma team celebrates its success; distributes rewards for active team members; and finally the Six Sigma Green Belt Certification Ceremony is undertaken.


Improve phase is the fourth phase of Lean Six Sigma projects. Following are the deliverable of this phase:

  • Identify Solutions to overcome the impact of root causes
  • Refine Solutions (FMEA, Poka-Yoke)
  • Pilot Solutions
  • Statistically validate results

Identify Solutions to overcome the impact of root causes

For each of the root causes identified in the Analyze phase, the Lean Six Sigma Team uses an apt structured or unstructured brainstorming method to generate various alternatives to overcome the problem. These techniques may include Channeling, Anti-solutions, Analogy, Wishful thinking, Random word stimulus methods, etc.
SCAMPER is another popular method which can be used by the Six Sigma Green Belt to systematically improve the current process using any of the following methods: Simplify or Substitute, Combine, Adapt, Modify, Put to different use, Eliminate & Reduce.
If there are too many options that the team has identified, then a variety of solution screening methods can be used to select the best solution for implementation. These screening methods include NGT (Nominal Group Technique), N/3 Voting, Criteria Based Matrix (CBT), etc.

Proposed solutions can be a new process, technology change, policy changes, alterations of inputs, measurement system refinement, customer, employee or vendor education, etc. In such cases, either revised process map, future state value stream mapping,  etc., may need to be proceeded.
The solution that the team has selected should directly impact the CTQ of the project. Six Sigma Green Belt should validate this.

Refining the Solutions (FMEA, Poka-Yoke)

Before implementing solutions, the Six Sigma Green Belt needs to ensure that the proposed solutions are complete and well refined. This will ensure that there are no delays, rework during implementation, and the full impact on CTQ is derived. In order to do this, a tool called Failure Modes Effect Analysis (FMEA) is used. The main purpose of this tool is to assess all the risks involved with a solution, and how to mitigate them by refining the solution before implementation. Risk Priority Number (RPN) derived from FMEA helps in prioritizing the risks and acting on them in a systematic manner.

Mistake-proofing (Poka-Yoke, in Japanese) is a method used to ensure that the proposed solution doesn’t create additional defects or errors. This can be used in conjunction with FMEA.
Pilot Solutions
Now the solution is ready for pilot. The purpose of the pilot is to assess its impact in a control group setting. Based on the qualitative and quantitative results of the pilot, necessary alternations can be incorporated to the final solution. Six Sigma Green Belt should closely work with the process owners during pilot to understand ground realities and build ownership.

Statistically validate results

In Lean Six Sigma Projects, it is an important step to statistically validate the impact on CTQ (before implementation & after Implementation). Hypothesis tests like 2-t test, ANOVA, Chi-square tests, etc., are used to perform this statistical validation. These tests help to identify if the improvement is significant or marginal in nature. Six Sigma Green Belt should be able to select and perform appropriate tests using statistical softwares.
On successful completion of these deliverable and formal Improve tollgate review, the Lean Six Sigma project team is ready to move to the Control phase.   Next >>>


Define Phase is the first phase of Lean Six Sigma Project. Following are the deliverable of this phase:

Develop the Project Charter

Project Charter is an important document that summarizes the purpose, current scenario & goal, measures of success (CTQ), project’s scope, quantitative & indicative project benefits, and team members. This is the most important document, as it creates a term of reference for this entire Lean Six Sigma project. In order to prepare the project charter, several meetings and preparatory steps may be needed. In some cases, gathering the Voice of Customer (VOC) may be required to even understand the problem.
Project Scoping determines exactly how the project will contribute to overall business, whether the efforts will be diverted to maximum impact area, team composition, financial resources required, etc. In Six Sigma, a tool called ‘In-Frame Out-Frame’ is used to decide on the scope.
Six Sigma Green Belt should closely work with the Project Sponsor to complete the Project Charter.

Identify the Project CTQ

CTQ refers to Critical to Quality metric. This is a measure of success for the project. Usually, there is only one CTQ for DMAIC projects. It can either be a measure of efficiency or effectiveness. However, it is a key performance indicator for Voice of Customer or Voice of Business. Further, it should be measurable. Usually, its indicative or accurate current performance is reported in the project charter.
The above two deliverable run parallel, and they are of significant importance because they mark the formal kick-off of the project, team member induction, Lean Six Sigma training (if not included earlier).

Create Process Maps

In order to understand the end-to-end process; a detailed process document is created by the team. However, in case such documentation already exists, then it becomes easy for the project team members to revisit it.

Process maps can be either high level end-to-end process documentation such as SIPOC (Suppliers, Inputs, Process, Outputs & Customers), deployment process-charts which use Swim-lane technique or step-by-step process flow-chart.  In some cases, just mapping the process itself can result in meeting the Lean Six Sigma project objectives!

Six Sigma Green Belt can involve all her team members in this activity. Two best ways of mapping a process are to interview all the parties involved in the process or to conduct a work-out session with all parties. Latter requires good facilitation skills.
Once the process maps have been created, the team can use them to identify the bottlenecks, challenges, issues, inputs & outputs, delays, etc. Essentially, it can be used to decide which part of the process is important, and needs to be introspected.
On completion of the above deliverable, a formal define tollgate review is conducted. Then the project moves to Measure Phase. Next >>>


Design for Six Sigma (DFSS) is an approach that is part of the Six Sigma methodology, and it aims to develop products and services which operate at Six Sigma or above. What does this mean; and how is this approach different from implementing six sigma in existing products, services & processes? If you have read our articles What is Six in Six Sigma, and What is Sigma in Six Sigma; you will understand how Six Sigma is measured.
Every process performs at its designed and operating capability. For instance, consider the Indian traffic and transportation management system. A good measure of its performance is the number of deaths due to road accidents. There are several other measures, but for simplicity let’s just consider this one. This performance measure is called CTQ (Critical To Quality).
India has the largest number of deaths per year due to road accidents (Approximately 130,000 deaths per annum). If we were to commence a Six Sigma project to reduce the number of deaths, we would use DMAIC approach. We will identify root causes for this problem, and try to eliminate them with good and sustainable solutions. For instance, helmets and seat belts mandatory, enforcement of speed limits & drunken driving laws, additional traffic patrols, etc., may be few solutions we will implement.
By doing so, lets hypothetically assume that we have been able to reduce the number of deaths to 30,000 per annum, in 3 years’ time. However, we aren’t able to reduce it any further. This stage; when any process or system is delivering its best performance, is referred to as Process Entitlement.
However, 30,000 is still a high number and we want to bring it down to manageable double digits. So we have to discard our existing traffic & transport management system; and design a completely new system, from scratch, that will help us reach our target. Double digit fatality means we will operate well within Six Sigma level, considering our 1.2 billion population as a base.
Such a process of re-designing or newly designing any product, service or products is referred to as DFSS. Design for Six Sigma is defined as a Customer focused design approach used for creating products, services, and processes which will deliver Six Sigma Performance. Samsung products are a very good example of Design for Six Sigma.
In many fields like airline, surgery, automobile braking, etc., require processes to deliver Six Sigma at all times. For such systems, design for six sigma concept comes handy. The very first time products and processes are developed, they are designed to deliver Six Sigma performance.
Following are the key differentiators for DFSS:

  • Understand customer requirements, and translate them to product performance measures.
  • Design products, sub-systems, and processes to deliver Six Sigma performance.
  • Design ‘first time right’ products and services.
  • Innovative designs deliver Six Sigma performance, rather than existing designs.
  • Optimize the design for usability, manufacturability, or serviceability.

While DFSS is a principle, there are different ways in which it can be put to use. IDOV and DMADV are popular approaches.
IDOV is a 4 step approach representing Identify, Design, Optimize & Verify.  And DMADV is a 5 step approach representing Define, Measure, Analyze, Design & Verify.


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