Quality Tools and Techniques
What the candidate must understand
Know the basic quality tools and when each applies: check sheet, flowchart, histogram, Pareto chart, cause-and-effect diagram, scatter diagram, and control chart, plus run charts and stratification. In auditing, flowcharts and process (turtle) diagrams map what should happen; Pareto charts rank where findings cluster; 5 Whys and fishbone diagrams push from symptom to root cause; FMEA and 8D support corrective action; control charts separate common from special cause variation.
Understand sampling. Acceptance sampling plans (for example ANSI/ASQ Z1.4) carry producer risk (rejecting a good lot) and consumer risk (accepting a bad lot). Audit sampling is usually attribute-based and must be representative: random, systematic, or stratified, never merely convenient. Increasing sample size reduces sampling risk but never eliminates it.
Traps that show up in questions
- Confusing a histogram (distribution of data) with a Pareto chart (issues sorted in descending order to drive prioritization).
- Treating AQL as a target defect rate; it is the quality level tied to a defined acceptance risk, not a goal.
- Confusing control limits with specification limits; limits come from the process, specifications from the customer.
- Assuming correlation proves causation when reading a scatter diagram.
- Stopping 5 Whys at a person or at retraining when the answer should be a system gap.
- Believing a larger sample removes sampling risk entirely.
Rule of thumb
For every finding, keep asking why until the answer is a changeable system condition. Example: 60 audit findings, 38 in document control - a Pareto chart shows document control is the vital few, so sample five randomly chosen records there, then run 5 Whys before writing the corrective action request.