ASQ Six Sigma Green Belt Body of Knowledge 2026: All 6 DMAIC Domains Explained

What Is the ASQ CSSGB Body of Knowledge?

The ASQ Certified Six Sigma Green Belt Body of Knowledge (BOK) is the official blueprint that defines every topic, tool, and concept tested on the CSSGB exam. Published by the American Society for Quality, the current BOK version took effect in August 2022 and remains the active framework through 2026. If you are preparing for the exam, the BOK is not just a study guide suggestion — it is the definitive outline of what ASQ considers essential knowledge for a practicing Green Belt.

The BOK organizes all exam content into six domains that follow the DMAIC methodology: Define, Measure, Analyze, Improve, and Control, plus an overarching domain covering Six Sigma fundamentals and organizational context. Each domain carries a specific percentage weight that determines how many of the 110 multiple-choice questions you will encounter from that topic area. Understanding this structure is the single most important step in building an effective study plan.

Whether you are just beginning to explore how to pass the ASQ Six Sigma Green Belt exam or you are deep into review sessions, this guide breaks down every domain so you know exactly what ASQ expects you to demonstrate on exam day.

BOK Structure and Exam Domain Weights

The CSSGB exam contains 110 multiple-choice questions, of which 100 are scored and 10 are unscored pretest items used for future exam development. You will not know which questions are unscored, so treat every question as if it counts. The total appointment time is 4.5 hours, giving you 4 hours and 18 minutes of actual testing time.

Notice that the Define and Measure phases together account for 40% of the entire exam. This is not an accident — ASQ believes that properly scoping a project and establishing reliable measurement systems are where Green Belts deliver the most organizational value. For a deeper look at exam weighting and what it means for your preparation, review our analysis of CSSGB exam difficulty and pass rates.

Domain	Exam Weight	Approx. Scored Questions	Key Focus Areas
1. Overview	11%	~11	Six Sigma history, Lean principles, team dynamics
2. Define	20%	~20	Project charters, VOC, SIPOC, stakeholder analysis
3. Measure	20%	~20	Process mapping, data collection, MSA, capability
4. Analyze	18%	~18	Hypothesis testing, regression, root cause analysis
5. Improve	16%	~16	DOE, Lean tools, Kaizen, solution selection
6. Control	15%	~15	SPC, control plans, sustaining improvements

Domain 1: Overview — Six Sigma and the Organization (11%)

Domain 1 sets the foundation for everything that follows. It covers the origins and evolution of Six Sigma, the organizational structures that support deployment, and the fundamental principles of Lean enterprise. While it carries the lowest weight at 11%, these questions tend to be conceptual and straightforward — making them easy points you cannot afford to miss.

Six Sigma Origins and Value

Expect questions about the history of Six Sigma, including its development at Motorola and popularization at General Electric. You should understand the relationship between sigma levels and defects per million opportunities (DPMO), the meaning of a 1.5-sigma shift, and how Six Sigma drives bottom-line financial results. Know the difference between Six Sigma and Total Quality Management (TQM), and be prepared to explain why organizations invest in structured quality improvement.

Organizational Structure and Deployment

This subtopic covers the roles within a Six Sigma deployment: Champions, Master Black Belts, Black Belts, Green Belts, and Yellow Belts. Understand the responsibilities of each role and how they interact. You should also know how Six Sigma aligns with strategic planning, including how projects are selected and prioritized based on organizational goals.

Lean Principles in the Organization

The BOK integrates Lean concepts throughout, but Domain 1 specifically tests your understanding of the eight wastes (DOWNTIME or TIM WOODS mnemonics), value stream thinking, and the concept of continuous flow. If you are curious about how Lean and traditional Six Sigma overlap and diverge, our article on Six Sigma Green Belt vs Lean Six Sigma explores this distinction in detail.

Domain 2: Define Phase (20%)

The Define phase is tied with Measure as the highest-weighted domain on the exam. It focuses on scoping a Six Sigma project, understanding customer requirements, and building the business case for improvement. A deep study of this domain is essential — you can find a dedicated walkthrough in our CSSGB Define Phase study guide.

Project Identification and Voice of the Customer

The Define phase begins with understanding the Voice of the Customer (VOC). You need to know the tools for capturing VOC data — surveys, interviews, focus groups, complaint analysis — and how to translate vague customer needs into specific, measurable Critical to Quality (CTQ) requirements using a CTQ tree. Understand the Kano model for categorizing customer needs into must-be, one-dimensional, and attractive quality attributes.

Project Charter and Business Case

The project charter is the foundational document of any DMAIC project. Expect questions about its components: problem statement, goal statement, scope, timeline, team members, and financial impact. Know the difference between a good and bad problem statement. ASQ tests whether you can distinguish between a statement that describes a symptom versus one that clearly quantifies a measurable gap.

SIPOC and Process Overview

SIPOC (Suppliers, Inputs, Process, Outputs, Customers) diagrams provide a high-level view of the process under investigation. You should be able to construct and interpret a SIPOC, and understand when it is used versus more detailed process maps that come in the Measure phase.

Project Management Basics

Domain 2 also touches on project management tools including Gantt charts, tollgate reviews, and stakeholder analysis. ASQ expects Green Belts to manage project timelines and communicate progress effectively. If you are weighing the CSSGB against other project-related certifications, our comparison of CSSGB vs PMP explains how these credentials complement each other.

Domain 3: Measure Phase (20%)

The Measure phase is where Six Sigma becomes quantitative. This domain tests your ability to collect reliable data, map detailed processes, evaluate measurement systems, and calculate baseline process performance. Together with the Analyze phase, these statistical topics form the technical backbone of the exam — our guide to statistical tools you must know for the CSSGB provides focused preparation for these concepts.

Process Mapping and Documentation

Detailed process maps, value stream maps, and flowcharts are the workhorses of the Measure phase. Understand the standard flowchart symbols, swim lane diagrams for cross-functional processes, and spaghetti diagrams for physical workflow. Know when to use each type and what insights each provides.

Data Collection and Sampling

You must understand data types (continuous vs. discrete, attribute vs. variable), sampling strategies (random, stratified, systematic), and how to design a data collection plan. Questions often test whether you can identify the appropriate data type for a given scenario and select the right sampling method to ensure representative data.

Measurement System Analysis (MSA)

MSA, particularly Gage Repeatability and Reproducibility (Gage R&R) studies, is a critical topic. You should understand the difference between repeatability (variation from the gage) and reproducibility (variation from the operators), how to interpret Gage R&R results, and what constitutes an acceptable measurement system. The general guideline is that measurement system variation below 10% of total variation is acceptable, 10-30% may be acceptable depending on the application, and above 30% requires improvement.

Process Capability and Performance

Capability indices Cp, Cpk, Pp, and Ppk are heavily tested. Know the difference between capability (within-subgroup variation) and performance (total variation), what each index tells you, and how to interpret values. A Cpk of 1.33 or higher generally indicates a capable process. Understand the assumptions behind these calculations, particularly the requirement for normally distributed data.

Domain 4: Analyze Phase (18%)

The Analyze phase is where you identify root causes using statistical evidence. At 18% of the exam, this domain demands competence in hypothesis testing, regression, and graphical analysis. Many candidates find this the most challenging section due to its statistical rigor.

Exploratory Data Analysis

Before performing formal statistical tests, Green Belts use graphical tools to explore data patterns. Know how to interpret histograms, box plots, scatter diagrams, run charts, Pareto charts, and multi-vari studies. Understand what each chart reveals about the data — central tendency, spread, shape, outliers, trends, and relationships between variables.

Hypothesis Testing

Hypothesis testing is a cornerstone of the Analyze phase. You must understand the framework: null hypothesis versus alternative hypothesis, Type I (alpha) and Type II (beta) errors, p-values, significance levels, and statistical power. Know which test to apply based on data type and comparison being made:

• 1-sample t-test: Compare a sample mean to a known value
• 2-sample t-test: Compare means of two independent groups
• Paired t-test: Compare means of paired or matched observations
• One-way ANOVA: Compare means across three or more groups
• Chi-square test: Test association between categorical variables
• Proportion tests: Compare proportions between groups

Correlation and Regression

Understand the difference between correlation and causation. Know how to interpret the correlation coefficient (r), the coefficient of determination (r-squared), and simple linear regression output. Be able to read a fitted line plot and residual analysis to assess model adequacy.

Domain 5: Improve Phase (16%)

The Improve phase translates analysis into action. This domain covers experimental design, Lean improvement tools, and solution selection and implementation. For a thorough treatment of these topics, see our dedicated article on DOE, Lean tools, and Kaizen concepts for the CSSGB exam.

Design of Experiments (DOE)

DOE is one of the most technical topics on the exam. At the Green Belt level, you need to understand the terminology and interpretation rather than complex calculations. Know what factors, levels, responses, main effects, and interactions are. Understand the difference between full factorial and fractional factorial designs. Be able to interpret a main effects plot and an interaction plot. Know why DOE is preferred over one-factor-at-a-time (OFAT) experimentation.

Lean Improvement Tools

Several Lean tools appear in the Improve phase: 5S (Sort, Set in order, Shine, Standardize, Sustain), Kaizen events, mistake-proofing (poka-yoke), pull systems, kanban, and setup reduction (SMED). Understand the purpose and application of each. ASQ often tests these through scenario-based questions — given a described problem, which Lean tool is most appropriate?

Solution Selection and Implementation

Not every identified improvement is worth pursuing. This section covers prioritization matrices, cost-benefit analysis, failure mode and effects analysis (FMEA), and pilot testing. Know how to calculate a Risk Priority Number (RPN) in an FMEA: Severity × Occurrence × Detection. Understand how to plan and execute a pilot run before full-scale implementation.

Domain 6: Control Phase (15%)

The Control phase ensures that improvements are sustained over time. At 15% of the exam, this domain focuses on statistical process control (SPC), control plans, and methods for maintaining gains. Our in-depth article on the CSSGB Control Phase: SPC charts, control plans, and sustaining improvements covers each of these topics thoroughly.

Statistical Process Control Charts

SPC is the backbone of the Control phase. You must know the different types of control charts and when to use each:

Chart Type	Data Type	What It Monitors	Subgroup Size
X-bar and R	Continuous	Mean and range	Small (2–10)
X-bar and S	Continuous	Mean and std deviation	Large (>10)
I-MR (Individuals)	Continuous	Individual values and moving range	1
p chart	Attribute	Proportion defective	Variable
np chart	Attribute	Number defective	Constant
c chart	Attribute	Count of defects	Constant area of opportunity
u chart	Attribute	Defects per unit	Variable area of opportunity

Beyond knowing chart selection, understand the rules for detecting out-of-control conditions. The Western Electric rules (also called Nelson rules) identify non-random patterns: points beyond control limits, runs above or below the center line, trends, and zone violations. Be able to look at a control chart and identify whether the process is in statistical control.

Control Plans and Documentation

A control plan documents how improvements will be monitored and maintained. Know the elements of a control plan: process steps, key input and output variables, specifications, measurement methods, sample sizes and frequencies, control methods, and reaction plans. Understand the connection between the control plan and the process FMEA developed in the Improve phase.

Sustaining Improvements

This subtopic covers the transfer of process ownership, training and documentation updates, lessons learned, and project closure. ASQ tests whether you understand that improvements must be institutionalized through standard operating procedures, training programs, and ongoing monitoring to prevent regression to old practices.

How to Study by Domain Weight

With the BOK structure clearly mapped, the question becomes how to allocate your study time. A common mistake is spending equal time on each domain. Instead, weight your preparation according to exam percentages — with adjustments for your personal strengths and weaknesses.

For a week-by-week breakdown of how to cover all six domains efficiently, follow our structured 8-week CSSGB study plan. And once you feel ready, test your understanding with our free CSSGB practice questions that mirror the actual exam format and difficulty level.

Frequently Asked Questions