Lean Six Sigma Green Belt Interview Questions

Q. What is Six Sigma?
Six Sigma (6σ) is a set of techniques and tools for improving the quality of processes. This data-driven and disciplined methodology can be used in any process, from manufacturing to transactional and from product to service. It was first introduced by Bill Smith while working in Motorola in 1986, and over the years, it has gained popularity in different industries and sectors for business improvement.

The Six Sigma concept as a prominent business methodology was derived to improve a product/service/process quality. Further, Six Sigma approaches were merged with the concept of process control, maximized productivity, and reduced waste.

There are many advantages to using Six Sigma, and its positive effects have been the driving force in the effective functioning of many businesses.

Q. Name some of the critical principles of Six Sigma.
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


Q. What is meant by COPQ in Six Sigma?
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


Q. What is the definition of DPMO or DPPM?
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

Q. What is the Pareto Principle?
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!

Q. Name some of the Quality Management tools in Six Sigma.
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)


Q. Name the different kinds of variations used in Six Sigma?
The different kinds of variation are —

  • Mean
  • Median
  • Range
  • Mode


Q. Who forms the part of the Six Sigma implementation team?
The Six Sigma implementation team usually consists of the following members:

  • Six Sigma Deployment Leader
  • Six Sigma Champion
  • Six Sigma Master Black Belt (MBB)
  • Six Sigma Black Belt (BB)
  • Six Sigma Green Belt (GB)
  • Six Sigma Yellow Belt (YB)


Q. What is the difference between the Six Sigma DMAIC and DMADV methodologies?
The DMAIC methodology, instead of the DMADV methodology, should be used when a product or process is in existence at your company but is not meeting customer specifications or is not performing adequately.

The DMADV methodology, instead of the DMAIC methodology, should be used when:

A product or process is not in existence at your company, and one needs to be developed.
The existing product or process exists and has been optimized (using either DMAIC or not) and still does not meet the level of customer specification or Six Sigma level. 


Q. Can you explain the concept of the fishbone/ Ishikawa diagram?
It is a visualization tool for categorizing the potential causes of a problem to identify its root causes.

Q. What is the load testing process?
It is the process of putting demand on a software system or computing device and measuring it.

Q. What level of understanding do you have regarding the statistical tools?
This answer for the interview question on Six Sigma should reflect the skills that you have regarding the statistical tools. Be honest while answering and give lots of examples.

Q. What is the difference between Cpk and Ppk?
Cpk is process capability index, which measures how close a process is running to its specification limits, relative to the natural variability of the process, and Ppk is process performance index, which verifies if the sample that has been generated from the process is capable of meeting Customer CTQs (requirements).

Q. Can you explain the standard deviation?
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.

Q. What is the process sigma calculation?
Process sigma is a measure of the variation in a process relative to customer requirements.

Q. What is the 1.5 sigma shift?
The 1.5 sigma shift adjustment takes into account what happens to every process over many cycles of manufacturing.

Q. What do you mean by MSA in a Six Sigma Green Belt project?

MSA refers to Measurement System Analysis which, refers to the analysis performed for verifying the measurement system for various parameters like accuracy, etc.


Q. What does Gauge R & R means in a Six Sigma Green Belt project?
The R & R expands to repeatability and reproducibility. The Gauge R & R is used to find the difference amongst the reproducibility and repeatability.


Q. What is Normal distribution in a six sigma green belt project?
The normal distribution or bell curve has data being centered around a central value without any bias. It is characterized with value of mean, median and mode being the same and has symmetry about the center with 50% of values less and greater than the mean.


Q. Calculate the mean and standard deviation for normally distributed data if 95% of policemen being 1.1m to 1.7m tall.

The Mean is: (1.1m + 1.7m) / 2 = 1.4m and 1 Standard deviation is = (1.7m-1.1m) / 4 = 0.15m


Q. What is Process Capability for a process in a six sigma green belt project
Process capability is the measurement of a process’s ability to output but within the specified limits consistently.


Q. What does Pareto Principle refers to?
The Pareto principle is also known as 80/20 rule and it states that 80 percent of the outcomes are due to 20 percent of causes.


Q. What is meant by standard deviation?


Standard deviation is the amount of variation of a set of values and a low value indicates data values are closer to mean and higher value indicates that data values are spread over a wide range.


Q. Explain process sigma calculation


Process Sigma indicates variation in a process against the requirements and is expressed as a number of standard deviations on a normal distribution.


Q. What is Regression?
Regression analysis shows the strength of relationships amongst a dependent variable and independent variable. It shows trends amongst two sets of data.


Q. Explain FMEA?
FMEA expands to failure mode and effects analysis, is an analysis technique to predict failures in a process or product and, prioritize failures as per probability and impact.


Q. Illustrate the X bar and R charts and their utility in a six sigma green belt project.
The X bar and R charts are control charts for processes having 2 or more subgroups. The X-bar chart displays changes in mean over time and the R chart displays changes in the range of the subgroups over time.


Q. What is brainstorming and its utility in six sigma green belt project?
Brainstorming is a group technique involving group of people to contribute ideas for solving a problem.


Q. What is Lean Six Sigma?
Lean Six Sigma involves combining lean and six sigma techniques to reduce waste and variations from a process or product.


Q. Describe VSM?
VSM or Value Stream Mapping is a technique to visualize all steps of a process to highlight the value-adding and wasteful steps.


Q. What is takt time?
Takt time refers to time taken for meeting the customer demand vis-à-vis production i.e. product creation speed needed for fulfilling the customer demand. Its calculated by the formula: Time Available for Production/Customer’s Daily Demand


Q. Explain an affinity diagram and its use in a six sigma green belt project
An affinity diagram organizes ideas as per their affinity or similarity and their relationship. It is a creative group technique about a product, process or problem.


Q. What is a control chart in a six sigma green belt project
Control chart analyzes process changes over a time period. It is a time series graph with horizontal line visualizing trends with UCL (upper control limit) and LCL (lower control limit)


Q. Differentiate between a Histogram plot and Box plot
A histogram plot shows the distribution of the data whereas a box plot compares multiple data sets with lesser space and details.


Q. Differentiate amongst the control and run chart
A run chart displays single data group variation over time to show trends in the process and process shifts. A control chart is similar to run chart but has UCL and LCL with a centreline and confirms if process is under control or going in correct direction or output is within limits.


Q. Which statistical test verifies that the means is between 2 inter-related groups
The paired t-test verifies the means being in between the two inter-related groups.


Q. What is the use for the 5S methodology in a six sigma green belt project
5S is a lean technique to create and maintain a safe, clean and efficient workplace by eliminating wastes.


Q. What is OEE in six sigma?
OEE expands to Overall Equipment Effectiveness measures if planned production time being productive or how fast production with no downtime, produces the required goods. It is calculated as: (Good Count or goods without defects× Ideal Cycle Time)/ Planned production time

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