Quality control and quality assurance
Design & Technology · Key Stage 3 · The School
Two different targets
QUALITY CONTROL (QC) checks the finished product. It measures, tests or looks at a sample of output for faults, and rejects or fixes anything that fails. QUALITY ASSURANCE (QA) instead looks at the PROCESS. Are the machines set up right? Are staff trained properly? Does the material meet spec when it arrives? QA aims to stop a fault happening at all, rather than catching it afterward.
Why prevention beats detection
A fault caught by quality control has already wasted the material, energy and time that went into making that faulty item. That cost is gone, even if the fault never reaches the customer. A fault stopped by quality assurance never wastes that cost in the first place. This is why makers invest heavily in QA, even though QC still stays necessary as a safety net.
Sampling in quality control
Checking every single item is often too slow or too costly for high-volume production. So QC often uses SAMPLING instead: checking a representative sample from a batch, not every item, and using statistics to judge whether the whole batch is likely fine. A well-chosen sample can catch a systemic problem without the cost of checking everything.
A bottle factory uses QUALITY ASSURANCE first. Each morning, before production starts, it calibrates its moulding machines. It trains staff on the right settings. It checks incoming plastic pellets meet spec before they are even used. All of this aims to stop a faulty bottle ever being made. It also uses QUALITY CONTROL. It pulls one bottle in every hundred off the line, and measures its wall thickness, weight and clarity against the spec. This catches any fault that slipped past the prevention step. If the sampled bottles start failing, that itself is useful news. It signals something in the PROCESS has likely gone wrong. Staff then go back and check the assurance steps, rather than just rejecting more finished bottles. QC and QA feed into each other. They are not two separate, unconnected checks.