IQ / OQ / PQ
Installation, operational and performance qualification. Proof that a system is installed right, works right, and works right for your process.
The three-letter ladder splits verification into layers: IQ confirms the system is installed as specified, OQ confirms functions operate as intended across their ranges, and PQ confirms the system performs in the real process with real users and real data.
Modern risk-based practice often merges or renames the layers, and CSA cares far more about whether high-risk functions got rigorous testing than what the protocol was called. The vocabulary survives because it gives auditors and engineers a shared map of what was proven where.
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