One inspected item can have more than one problem. A report becomes ambiguous when the number of issues is presented as though it were the number of affected units.
ASQ's statistical process control resources discuss using process data and appropriate statistical methods to understand variation. ASQ — statistical process control.
State the counting rule
For an illustrative inspection, decide whether the measure counts nonconformities, units with at least one nonconformity or another defined outcome. Record the inspected population and denominator. These are different measures even if the totals happen to match on one occasion.
Preserve useful detail
A unit-level decision may be needed for disposition, while issue-level counts may help identify recurring causes. Keep both where relevant instead of overwriting one with the other. Do not compare reports until their counting rules and inspection boundaries align.
This distinction makes quality discussions more precise. It also prevents a change in reporting practice from being mistaken for a real improvement or deterioration in production.
Source reviewed 25 October 2026. Practical interpretation and original illustrations by PLUSHIP / Qunhe; examples are illustrative.
Related reading
Quality Assurance and Quality Control Address Different Questions
Quality Cost Includes More Than Rejected Products