Section V: Improve Phase 16 questions
Improve carries 16 of the 100 scored questions on the 2022 CSSGB exam. It covers the basics of design of experiments (DOE) and the lean tools a Green Belt uses to remove waste and cut cycle time, including kaizen.
Key topics
| Topic | What to know |
|---|---|
| Design of experiments: basic terms | Factors, levels, response, treatment, replication, randomization, blocking, main effects, interactions, and the idea of a full factorial (2k) design. |
| DOE graphs and plots | Main effects plots and interaction plots: read which factors matter and whether they interact. |
| Waste elimination | The eight wastes; tools such as 5S, standard work, pull and kanban, and mistake-proofing (poka-yoke). |
| Cycle-time reduction | Continuous flow, reducing batch sizes and queues, setup reduction (SMED, single-minute exchange of die). |
| Kaizen | Continuous small improvements and short, focused kaizen events (kaizen blitz). |
Solution selection and piloting are not separate BoK headings, but you need them to get through the Improve tollgate in practice.
DOE: reading a 2² experiment
Factors A (temperature) and B (speed), each at low (−) and high (+): A− B− = 20 A+ B− = 30 A− B+ = 24 A+ B+ = 40 Main effect A = avg(A+) − avg(A−) = (30+40)/2 − (20+24)/2 = 35 − 22 = 13 Main effect B = avg(B+) − avg(B−) = (24+40)/2 − (20+30)/2 = 32 − 25 = 7 Interaction AB = (20+40)/2 − (30+24)/2 = 30 − 27 = 3
On an interaction plot, roughly parallel lines mean little interaction; crossing or strongly diverging lines mean the effect of one factor depends on the level of the other.
The 8 wastes (DOWNTIME)
| Letter | Waste | Example |
|---|---|---|
| D | Defects | Rework, scrap, correcting errors |
| O | Overproduction | Making more, or sooner, than demand requires |
| W | Waiting | People or work idle, waiting for approvals, machines, information |
| N | Non-utilized talent | Ignoring employee ideas and skills |
| T | Transportation | Moving materials or products unnecessarily |
| I | Inventory | Excess raw material, WIP or finished goods |
| M | Motion | Unnecessary movement of people: walking, reaching, searching |
| E | Extra processing | Work the customer does not require, such as duplicate approvals |
Takt time and cycle time
Takt time = available production time ÷ customer demand 450 min/day available, 90 units/day demand → takt = 5 min/unit Cycle time > takt: the step cannot keep up without overtime or added capacity Cycle time < takt: spare capacity; risk of overproduction if you build ahead
Mistake-proofing
Preventing an error (a jig that only accepts the part in the correct orientation) is stronger than detecting it after it happens (a sensor that rejects a misassembled unit), which in turn beats a warning that relies on someone noticing it. Redesigning the step so the error cannot arise at all is strongest.
Common exam traps
- Motion vs. transportation. People moving → motion; materials moving → transportation.
- Overproduction is traditionally called the worst waste because it creates others (inventory, transport, hidden defects).
- Randomize run order in a DOE to protect against lurking time-related variables; replicate to estimate experimental error.
- Pilot before full rollout to confirm the improvement and catch side effects.
Learn pages for this section
The free 20-question CSSGB diagnostic covers all six sections and shows your score by section.
Take the free diagnostic →Section names and question counts follow the 2022 CSSGB Body of Knowledge (110 questions, 100 scored). Topic summaries are our paraphrase; check the current BoK on asq.org for the official wording.
CSSGB Quest by Bizarre Act. Original study material; not affiliated with ASQ. CSSGB is a certification of ASQ. Terms · Privacy