Six Sigma Specialist: Interview Questions and Answers

Six Sigma is a mathematical and process-driven methodology with a specific approach to handle defects. In comes in many skill levels -such as Green Belt, Black Belt, Master Black Belt- and other variations, such as Lean Six Sigma. Having Six Sigma attached to your resume showcases your talent for identifying gaps and waste in processes and improving business operations by being able to increase productivity and efficiency.
In this article, you can go through the set of Six Sigma interview questions most frequently asked in the interview panel. Let us have a quick review of the Six Sigma interview questions.

Ans. Six Sigma is a set of techniques and tools for process improvement. Six Sigma strategies seek to improve the quality of the output of a process by identifying and removing the causes of defects and minimizing impact variability in manufacturing and business processes. It uses a set of quality management methods, mainly empirical, statistical methods, and creates a special infrastructure of people within the organization who are experts in these methods. Each Six Sigma project carried out within an organization follows a defined sequence of steps and has specific value targets, for example: reduce process cycle time, reduce pollution, reduce costs, increase customer satisfaction, and increase profits.

The benefits of the six sigma process are as follows:
• Helps the organization to reduce to a level where they can eliminate the errors.
• Works towards improving the business processes.
• Works towards the betterment of Quality Assurance.
• This process can be applied throughout the business environments, applicable for all the markets.
• Makes sure that it comes under compliance.
• Helps the individuals to build skills and turn them into leaders.
• Have attractive salaries for individuals having this skill.
• Quality assurance and quality management.

Ans. Mainly 4 variations are used in six sigma process:

• Mean: This measurement is only useful for a particular application and the values are calculated. In this process, the variations are measured and compared using the average techniques of mathematics.
• Median: This process is initiated by identifying the highest and the lowest values and then divide the value by 2. In this process, the variations are measured and compared by taking the midpoint the data set range.
• Range: This process depends on the highest rate and lowest values for a specific data range.
• Mode: Mode is the most occurred values in a given data set range.

Ans. Six Sigma is used to match the most prominent word called ‘perfection.’ Following are some of the promising principles of six sigma:
• Primary focus on customer requirements
• Relying on statistical analysis to find out the best possible ways of working and identifying root causes of probable problems
• Process improvement
• Formulate flexibility in processes
• Effectively managing cross-functional teams

Ans. Cost of Poor Quality (COPQ) is the cost caused by producing defects. This cost involves the following parameters:
• Filling the gap between the desired and actual product/service quality
• cost of lost opportunity
• Labor cost
• Rework cost
• Disposition costs
• Extra material costs
• Loss of sales/revenue
• Cost of extra utilities
COPQ does not include:
• Detection cost
• Prevention cost

The interviewer wants to know if you have ever tried to think about why only Six Sigma and not beyond. You should analyze the answer to this question by yourself, why 6 why not 7, not 5? Here we can say that while achieving the Six Sigma, the yield would be 99.9996%, which is hard to achieve otherwise as we need to commit to only 3.4 defects, the target must be difficult and achievable and therefore it is Six Sigma.

For this question, you must describe the projects which you really worked upon and you have very good insight into. This is very important as the answer to this question will decide the direction in which the rest of your interview goes.

These things depend upon the benefits we would get after the projects and the area of projects. If the scope of the project is at the company level, it should be counted as a Black belt project. However, if it is limited to one single process, it would be considered as a Green Belt project.

To answer these Six Sigma Interview Questions mention the problems that you must have faced during the project. Then share the ways you overcame those issues.
If you have worked on a project, then try to recall major to minor details while working on the Six Sigma project. Write down some points that are important and also some factors that are basic in Six Sigma projects. It will help you to answer interview questions concerning your project.
For the next set of questions, I have listed some Six Sigma Interview Questions and Answers concerning minor and important factors of Six Sigma. Have a look!

In Six Sigma process, it depends upon the methodology, either DMAIC or DMADV, and for each stage, there should be some time durations involved, the milestones provide the time duration limit for each stage, if we extend the time limits, we need the approval from stakeholders.

The problem should be clear and crisp and should be defined in metrics so that it is easier to make the stakeholders understand what would happen if the problem has not been resolved, the future consequences also should be shared with stakeholders.

Ans. DPMO is Defects Per Million Opportunities, and DPPM is Defective Parts Per Million.
Here the defects are inclusive of flaw or discrepancy (more than one flaw) on an item.
The formula of PPM is = (Total number of defective units in a sample/ sample size) * 1,000,000

Ans. The DMAIC project methodology has five phases:
• Define the system, the voice of the customer and their requirements, and the project goals, specifically.
• Measure key aspects of the current process and collect relevant data; calculate the 'as-is' Process Capability.
• Analyze the data to investigate and verify cause-and-effect relationships. Determine what the relationships are, and attempt to ensure that all factors have been considered. Seek out the root cause of the defect under investigation.
• Improve or optimize the current process based upon data analysis using techniques such as the design of experiments, poka-yoke or mistake proofing, and standard work to create a new, future state process. Set up pilot runs to establish process capability.
• Control the future state process to ensure that any deviations from the target are corrected before they result in defects. Implement control systems such as statistical process control, production boards, visual workplaces, and continuously monitor the process. This process is repeated until the desired quality is achieved.
On the other hand, DMADV methodologies five phases are:
• Define design goals that are consistent with customer demands and the enterprise strategy.
• Measure and identify CTQs (characteristics that are Critical To Quality), measure product capabilities, production process capability, and measure risks.
• Analyze to develop and design alternatives
• Design an improved alternative, best suited per analysis in the previous step
• Verify the design, set up pilot runs, implement the production process and hand it over to the process owner(s).

Ans Fishbone or Ishikawa diagram is a visualization tool for categorizing the potential causes of a problem in order to identify its root causes.

Ans. The load testing process is a process of putting your demand on a software system or computing and measuring its process.

Ans. Performance Testing is a type of software testing that can be carried out to measure the system performance in terms of sensitivity, reactivity, and stability under a particular workload.
On the other hand, The load testing process is a process of putting your demand on a software system or computing and measuring its process.

Ans. The Pareto principle (or the 80/20 Rule) states that, for many events, roughly 80% of the effects come from 20% of the causes. For example:
• 20% of the input = 80% of the result
• 20% of the workers’ efforts deliver = 80% of the result
• 20% of the customers results in = 80% of the revenue
• 20% of the bugs cause = 80% of the crashes
• 20% of the features cause = 80% of the usage
However, people’s misconception is that 20 + 80 = 100 - however it’s not always accurate because most things are not 1/1.
That’s where the Pareto principle works:
• If 20% of workers deliver 80% of the results, 20% of people should be rewarded.
• If 20% of the clients contribute to maximum revenue share, the idea is to keep these clients satisfied and motivated to buy
The Pareto principle (it’s just an observation and not law) says that one must realize focusing upon the overall efforts contributed by the 20%s instead of wasting must time on 80%. Near to perfection, it is!

Ans. There are several quality management tools. Some of them are:
• Cost-benefit analysis
• CTQ Tree
• SIPOC analysis
• COPIS analysis
• Taguchi methods
• 5s
• Seven wastes
• Value stream mapping:
• Visual workplace
• Quality function deployment (QFD)

Ans. In Six Sigma, the P-value refers to the probability value, which determines the significance of results based on the null hypothesis. The null hypothesis states the cause of the event was not established; hence in reality, the statement which one tries to prove did not happen.
P-value falls between 0 and 1 and if the p-value is:
•
o Less than 0.5 - the event has a substantial value against the null hypothesis; hence it is significant as per statistics.
o Greater than 0.05 - the event has a substantial value for the null hypothesis; hence alternative hypothesis gets rejected
However, it is not suggested to entirely rely on P-value. One must also cater to calculate the effect size.

Ans. Effect size refers to the measure of the overall magnitude experiment effect, which is quantitative. The larger the size of the impact, the better falls the relationship between the given variables. In simpler terms, the calculation of effect size results in formulating the relationship between different variables.

Ans. The 3 steps for Root cause analysis are:
• The Open step: In this step, all the team members gather together and do a brainstorming session on all possible scenarios.
• The Narrow step: They narrow down all the possible explanations and scenarios are to an extent considering the current performance.
• The close step: The project team validates all the narrowed down explanations for the current performance.

Ans. Six Sigma follows the DMAIC methodology to reduce waste. On the other hand, Lean uses these following 7 steps:
1. Overproduction: This occurs when products are being produced but there is no customer to demand it.
2. Waiting: If there is a time lag after every step of production, no value is being to the project in the meantime.
3. Transport: This happens when products are being moved in an inefficient way.
4. Motion: This one denotes poor work standards and employees being involved in inefficient activities between tasks.
5. Over-processing: This takes place when you spend too much time in producing a product.
6. Inventory: When your inventory level is too high and you have too much work in progress, this kind of waste takes place.
7. Defects: This is the number of times when employees spend identifying and fixing production mistakes.

Ans. Lean Six Sigma is a method that relies on a collaborative team effort to improve performance by systematically removing waste and reducing variation. It combines lean manufacturing/lean enterprise and Six Sigma to eliminate the eight kinds of waste: Defects, Over-Production, Waiting, Non-Utilized Talent, Transportation, Inventory, Motion, and Extra-Processing.

Ans. This is a popular Lean Six Sigma interview question. Below are some of the practical Lean Six Sigma projects:
o Quick win projects - Also known as ‘Just-do-it project’ as the problem is known and so is the solution. Thus the fix is painless
o Process improvement projects - Also known as PDCA, here the issue has an undefined cause leading to unsatisfactory results.
o Designing new process projects - Also known as DFSS, This involves creating a brand new process that does not exist previously. Thus, there is no benchmark process to compare with hence it requires a VOC.
o Redesigning new process projects - Also known as reengineering, this method focuses on overhauling processes that are proven completely ineffective.
o Implementing new infrastructures - Also known as process management, this step involves establishing key measurement systems.

Ans. Cpk stands for process capability index. It measures how close a process is running to its specification limits, relative to the natural variability of the process.
On the other hand, Ppk stands for a process performance index that verifies if the sample has been generated from the process is capable of meeting Customer CTQs or not.

Ans. A data collection plan a plan to collect the necessary data. The main reason to collect data is to understand the current process and portray possible improvement suggestions. The data can be collected from three different primary sources they are as follows:
1. Input: input is where the data generation.
2. Process: the process is the execution steps where the factors like efficiency, time requirements, cost, defects are taken into consideration for process improvements.
3. Output: it is a straight measurement of efficiency.

Ans.
A Histogram represents the frequency distribution of numeric data, while a Boxplot summarizes the important aspects of continuous data distribution.

Ans. The Six Sigma implementation team usually consists of the following members:
1. Six Sigma Deployment Leader
2. Six Sigma Champion
3. Six Sigma Master Black Belt (MBB)
4. Six Sigma Black Belt (BB)
5. Six Sigma Green Belt (GB)
6. Six Sigma Yellow Belt (YB)

Ans. Standard deviation indicates the degree of variation in a set of measurements or a process by measuring the average spread of data around the mean.

Ans. Process sigma is a measure of the variation in a process relative to customer requirements.

Ans. The 1.5 sigma shift adjustment takes into account what happens to every process over many cycles of manufacturing.

Ans. Regression Analysis is a technique used to define the relationship between an output variable and a set of input variables.
There are several types of regression like Simple Linear Regression, Multiple Linear Regression, Curvilinear Regression, Logit Regression, Probit Regression, etc., which cater to various requirements on the type of underlying data.

Data can be of two major types - Quantitative and Qualitative. Under the quantitative data comes the Continuous data and Discrete data attributed comes under the qualitative data category. This can be described in a more detailed manner.

MSA is Measurement System Analysis, using this we see whether our measurement system is correct or not. For service industries, we do the Attribute analysis.

In Gauge R and R, we gauge by repeatability and reproducibility. Here you need to describe the difference between the repeatability and reproducibility.

In Normal distribution, we see the p-value, and if it is not normal, we try to make it normal or transfer into the Box-Cox transformation.

Ans. VSM stands for Value Stream Mapping. This is a methodology used to eliminate wastes from a process and map the flow of information required to deliver a product or service.

Ans. SIPOC stands for Suppliers Input Process Output Customers.
It defines that a process can be summarized as a series of consecutive steps and activities that are executed in a timely manner to get a definite output.

If the data is non-normal, we need to try to make data normal, if we cannot, then we need to use the non-normal hypothesis testing, as per their subgroup size.
After the analyze phase, questions can be asked about what improvement plans you made, or the tools used. The improvement can be done using the FMEA, therefore we should know what is FMEA and what are the types of FMEA, what is RPN value and how to calculate it. We can also use the affinity diagram for the solution purpose, which can be done by brainstorming to resolve the issues.

Ans. This is one of the most important questions on Six Sigma. So be detailed with your answer. Kano is a product development tool used to identify the Voice of the Customer (VOC) and compares the characteristics versus the degree of satisfaction each characteristic delivers. The tool was invented by Dr. Kano which defines the following 5 characteristics:
• Dissatisfying
• Must-Haves
• Customer needs
• Delighters
• Indifferent

Ans. A spaghetti diagram is a part of lean tools that are used to eliminate different forms of waste. This tool helps in reducing wastes like transportation, motion, and waiting time. It tracks the movement of items like - product, paper, and/or people. It visually represents the details like flow, distance, waiting time, walking patterns of items/people. Using a spaghetti diagram offers the following benefits:
• Highlights inefficient areas/work layouts
• Highlights transport-related waste
• Reduces non-value items
• Reduces fatigue of people by minimizing moments
• Adds value to the concept of lean

The White Belt is the first and beginner level of Six Sigma. The professionals who have just entered their career in Six Sigma are at the White Level of Six Sigma. The professionals who hold the White Belt of Six Sigma begin to participate in problem-solving projects. They become aware of their contribution to efficient and most reliable outcomes.

A Yellow Belt holder of Six Sigma is one who has known the fundamentals of the White Belt level and now works as a project team member. The professionals at this level also assist those who are at the higher levels of Six Sigma.

Those who hold the Green belt of Six Sigma are the ones who have gained experience of at least 3-years working full-time. The holder of a Green Belt Six Sigma must have also completed at least one project of Six Sigma. They can also serve as a leader for simple Six Sigma projects.

Six Sigma Black Belt professionals are those who carry the experience of 3-years in full-time work. Those with the Six Sigma Black Belt certification also carry experience working on at least two projects. In their work experience, they have gained core knowledge in the area.

Six Sigma Master Belt professionals are those who carry five years of experience in full-time employment. They have worked on a minimum of 10 projects of Six Sigma. A Six Sigma Master Black Belt holder must have trained the Green Belts and the Black Belts. Six Sigma Master Black Belt is a position of an expert who has a wide array of experience and coordinates with all the functional team.

Six Sigma Champion is the one who takes care of the political aspect of a project. Using their political skills they make sure that their projects are successful. In a corporate world, many projects come in the way of one another either economically or in terms of priority, so it is the role of a Six Sigma Champion to use their political skills and clear out the matter to make their project successful.
These are some basic questions that an interviewer may ask you to check your knowledge and also to discern your understanding of the roles and functions played at various levels of Six Sigma.
In the next set of questions, I have listed questions that an interviewer may ask concerning the projects you have worked on.

Here we must give the details for control charts and all the rules, which we can see in Minitab and Nelson's rule.
Apart from these questions, they may ask a few more questions to check your six-sigma knowledge, like:

Control limits are process driven. It refers to the real-time value that the process is operating on. Whereas, the specification limit is given by the client and the process targets are set by the client based on market performance.

First, we need to see that process is in control or not (stability), and if data is normal or not, if the process is not stable, we cannot run the project, we need to make process stable, then we need to see the process normality, as per the process normality/non-normality we do the process capability to see whether the process is capable enough to run the project.

Ans. Using a SIPOC tool is recommended when the answers to the following situations are not very clear:
• Who offers the inputs for refining the process?
• Do you know which specifications are placed on the inputs?
• Who are your potential customers in context to these processes?
• What are the exact requirements of the customer?

Ans. Kaizen events are helpful in establishing incremental improvements. In the following situations using a Kaizen event turns out to be the best solution:
• When a quick solution to a pressing problem is needed
• When the impact of a problem turns appears to be very significant
• When the improvement is possible to be visible in three to five days
• When an intensive cross-functional collaboration is involved

Ans. A scatter plot is a graphical diagram representing two different variables. Usually, the independent variable lies on the horizontal axis, while the dependent variable lies along the vertical axis. It is easier and quicker to find a positive or negative correlation between the disparate variables.

Ans. When the data in the X-Y plane moves upwards from left to right, it is a positive correlation. Conversely, if the data moves downwards it is a negative correlation.

Regression analysis helps to establish the relationship between the output variable (Y) and input variables (X).

FMEA is abbreviated for Failure Mode and Effect Analysis. This analysis is used to identify possible risks within the process, design, or product. After identifying the possible risk, one can develop a risk mitigation plan to overcome these risks.

Ans. Zero Defects term was used by Mr. Philip Crosby in his book “Absolutes of Quality Management”. This concept is very popular and is a quest for perfection to improve quality. Below are some of the pros and cons of Six Sigma:
Pros:
• Offers enhanced value to the customer
• Reduces/eliminates hidden costs
• Helps in planning
Cons:
• Very difficult to attain
• Sound more abstract to most of the companies
• Outdated technology
• Tim bounded and requires a proactive approach

Ans. Here you can share your experience of why did you go for a black belt six sigma certificate. Some of the possible reasons are:
• A better understanding of Six Sigma principles
• Helpful in all industries
• Helps in organizational growth
• Helps in reducing error and improving quality in processes

Ans. A performance test checks a system’s responsiveness and reliability when it faces a higher workload. Load testing is a part of performance testing and one can implement it separately as well. In other words, load testing evaluates the system’s operating capacity, while performance testing determines whether or not the system functions properly.

Ans. RACI is the acronym for
Responsible - One who is assigned a task.
Accountable - One who assigns tasks to others.
Consulted - Subject matter experts who can guide those who are doing the tasks.
Informed - One who is informed a task is complete.
The RACI matrix brings clarity on an organisational level. It defines roles clearly and ensures proper teamwork, vital for project completion with efficiency.

Well, these are the individuals who will be responsible for driving initiatives to make sure their product quality and processes are optimized to a profitable level where the entire team is being productive with fewer operations costs incurred.
So most of the time, the executive leaders will be the CEO or Board of director members, etc. The main motto of these individuals is to make sure that they deliver a quality product to the customers and make sure they are satisfied.