Accuracy and Precision
Definition
Accuracy is closeness to the true value, measured as recovery from a spiked CRM with the 80 to 120 percent window. Precision is the spread of replicates as RSD: intra-day typically 1 to 5 percent for a well-tuned LC-MS/MS, inter-day 2 to 10 percent.
- Accuracy metric
- Percent recovery from a spiked CRM
- Accuracy window
- 80 to 120 percent
- Precision metric
- Relative standard deviation of replicates
- Intra-day RSD (LC-MS/MS)
- About 1 to 5 percent
- Inter-day RSD
- About 2 to 10 percent
Common questions
Why is inter-day precision typically worse than intra-day precision?+
Day-to-day variation adds sources of error such as fresh calibration curves and instrument drift on top of the random error already present within a single run.
What does falling outside the 80 to 120 percent recovery window mean?+
It suggests a systematic problem such as matrix interference, incomplete extraction, or analyte degradation, and the method or batch may need to be re-validated or re-run.
Why validate both accuracy and precision rather than just one?+
A method can be precise but biased, or accurate on average but too scattered to trust a single result, so both properties are needed before a method is certified fit for casework.
Related terms
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- Method Validation
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