Quality Basics
Core definitions
Quality is judged by the customer, not by the producer's intent. Two working definitions dominate: conformance to requirements (Crosby) and fitness for use (Juran). A product can be high grade (luxury features) and still be low quality if it fails requirements - grade and quality are not the same thing.
Customers and costs
Every process has internal customers (the next step downstream) as well as external ones. Prevention beats detection: it is cheaper to design quality in than to inspect defects out. Cost of quality splits into cost of good quality (prevention and appraisal) and cost of poor quality (internal failure such as scrap and rework; external failure such as returns, warranty, recalls, lost goodwill). Training, supplier evaluation, and process design are prevention; inspection and testing are appraisal.
Origins and frameworks
Know the major contributors: Deming (PDCA, 14 points, profound knowledge), Juran (quality trilogy: planning, control, improvement), Crosby (zero defects, cost of quality), Feigenbaum (total quality control), Ishikawa (cause-and-effect diagram, company-wide quality). ISO 9001 is a requirements standard for a quality management system, not a product standard or a performance award.
Traps
Questions often swap prevention and appraisal, or place warranty costs in internal failure. Watch for "quality means meeting specifications" offered as a complete definition - it ignores customer needs. Also beware answers that treat inspection as a quality improvement activity.
Rule of thumb
Ask where the cost occurred: before the customer saw the product (internal failure), after (external failure), or to stop it happening at all (prevention). Example: a batch scrapped in-house is internal failure; a unit replaced under warranty is external failure.