Uncertainty of a replicate mean
For n independent identically distributed observations of a stable quantity with finite variance, the replicate-mean standard uncertainty is estimated by s/√n, where s²=Σ_j(x_j−x̄)²/(n−1).
Key knowledge
For n independent identically distributed observations of a stable quantity with finite variance, the replicate-mean standard uncertainty is estimated by s/√n, where s²=Σ_j(x_j−x̄)²/(n−1). Under a normal sampling model, the variance estimate has n−1 degrees of freedom.
Values and equations
x̄=(1/n)Σ_jx_j; s²=Σ_j(x_j−x̄)²/(n−1); u_A(x̄)=s/√n
- x_j,x̄,s,u_A
- Observations, mean, sample spread and uncertainty; measurand unit
- n,j
- Replicate count and index
Conditions and scope
- n≥2, stable comparable replicates, no unmodeled drift or shared systematic effect in this repeatability component.
- Averaging does not remove common calibration uncertainty; correlated observations require the covariance of the mean. Normality is needed for the exact Student-t coverage statement, not for variance/n itself.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
National Institute of Standards and Technology (NIST)2 sources
Evidence and review
NIST TN 1297 (1994): Type A evaluation: Section 3: repeated observations, sample mean and estimated standard deviation of its mean. NIST TN 1297 (1994): Coverage factors: Appendix B.3: ν=n−1 for the replicate-mean component.
2026-10-10 · Independent AI editorial review: Independent root AI editorial review of all29 authored Measurement claims/conditions, displayed equations and37 origin relations. The original26 claims were read against41 primary source sections; all5 requested corrections and the3 affected source bindings were subsequently rechecked. Three actual scalar-nonlinear/vector/dynamic applications were read, independently differentiated or integrated, and checked against the specific additional source material described below. This is reference-content review, not human specialist certification, instrument certification or experimental replication. Full-field sign-off waits for the combined final conceptual matrix. Receipt: measurement-independent-content-review.1.
Entry details
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- measurement-repeat-sample-uncertainty
- Revision
- university-core.1
- Structured reference record
- University core expansion