Quality Tools and Techniques
Seven basic tools
- Flowchart: picture the process; find handoffs, loops, and non-value steps.
- Check sheet: structured tally of defect types, locations, or causes during data collection.
- Pareto chart: categories ranked by frequency with cumulative percentage; separates the vital few from the useful many.
- Cause-and-effect (fishbone): brainstormed causes grouped by category (people, machine, material, method, measurement, environment); it organizes hypotheses, not data.
- Histogram: distribution of a single variable - shape, spread, centering.
- Scatter diagram: relationship between two variables; correlation is not causation.
- Control chart: plots a process over time with control limits from the process itself; distinguishes common from special cause variation.
Also useful: run charts (time order without limits), stratification (split data by source before charting), 5 Whys, and FMEA.
Traps
Control limits are not specification limits; a process can be in control and still make bad product. A Pareto chart needs categories and counts; a histogram needs measurement data in bins. Choosing a fishbone when the question asks for data collection or prioritization. Points outside control limits signal special cause, not common cause.
Rule of thumb
Match the tool to the question: What does the process look like? Flowchart. What defect types and how many? Check sheet, then Pareto. What causes? Fishbone. Is the process stable? Control chart. Are two variables related? Scatter.
Worked example
A team tallies 500 complaints: late delivery 250, wrong item 125, damage 75, other 50. Cumulative percentages show late delivery plus wrong item at 75% - the vital few to attack first.