Quality Management
Concepts and calculations that can support laboratory quality control workflows.
Westgard Rules
Common statistical quality control rules used to review analytical results.
Measurement Uncertainty
An illustrative estimate using the calculation described on this page.
Core Statistics
ISO 15189 referenceThe foundation of all laboratory quality control begins with basic descriptive statistics.
The arithmetic average of your laboratory's actual QC results.
Standard Deviation derived from manufacturer reagent limits. Used for LJ grid lines.
Actual measured precision of your laboratory instruments.
Performance Metrics
Clinical StandardsHow well is your lab performing against manufacturer targets?
Measures the signed difference between the observed mean and the target mean.
Expresses systematic error as a relative percentage of the target mean.
Measures the relative precision of your QC runs.
Indicates how many standard deviations your mean is from the target.
Measurement Uncertainty (MU)
Official GUM ProtocolThis page illustrates a Root Sum Square (RSS) calculation combining observed standard deviation and bias. It is an educational simplification and should not be treated as a validated uncertainty budget or a claim of conformity with a standard.
1. Combined Standard Uncertainty (uc)
We use the root sum of squares (RSS) to combine precision (Observed SD) and systematic error (Bias).
2. Expanded Uncertainty (U)
By default, we use a coverage factor (k) of 2, which provides approximately 95% coverage under common normal-distribution assumptions in the reported range.
3. Relative Expanded Uncertainty (U%)
Expresses the expanded uncertainty as a percentage of the observed mean.
Levey-Jennings & Westgard
Westgard.com ReferenceThe application automatically monitors your data against standard Westgard rules:
Within limits: Result within ±2.0 SD.
Warning: Result beyond ±2.0 SD but within ±3.0 SD.
Out: Result exceeds ±3.0 SD (Westgard 13s). Review the result according to your laboratory's QC procedure.