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Posted on 04 Oct,2025
One of the key requirements of ISO/IEC 17025:2017 is the application of decision rules when reporting statements of conformity (e.g., pass/fail, compliance/non-compliance). This ensures that laboratories make technically valid and transparent judgments based on measurement results and associated uncertainty.
A decision rule is the rule or criterion used by a laboratory to decide whether a test or calibration result conforms to a specified requirement. It defines how measurement uncertainty is considered when comparing results against specification limits.
ยท They reduce the risk of false acceptance or rejection of results.
ยท Provide consistency and transparency in reporting.
ยท Help customers understand the confidence level behind conformity statements.
ยท Labs must apply appropriate decision rules when stating compliance with specifications.
ยท If no decision rule is prescribed by the standard, regulatory body, or customer, the lab must agree on the decision rule with the customer.
ยท The decision rule used must be clearly communicated in the test/calibration report.
1. Simple Acceptance Rule: Result is directly compared with the specification limit (ignores uncertainty).
2. Guard Banding: Adjusting acceptance limits to account for measurement uncertainty, reducing the risk of false decisions.
3. Shared Risk Approach: Assigning a certain probability of compliance (e.g., 95% confidence level).
ยท Understand customer and regulatory requirements.
ยท Evaluate and document the measurement uncertainty.
ยท Define and agree on the decision rule before testing/calibration.
ยท Apply the rule consistently and record it in reports.
Decision rules ensure that laboratories not only provide accurate results but also make defensible compliance decisions considering measurement uncertainty. For ISO/IEC 17025 accredited labs, mastering decision rules is crucial for credibility, customer trust, and compliance with the standard.
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