The standard uncertainty of the output quantity, written u_c(y), obtained by combining the standard uncertainties of all inputs, each multiplied by its sensitivity coefficient, as a root sum of squares plus covariance terms for correlated inputs. Three uncorrelated contributions of 3, 4 and 12 µm combine to 13 µm, which shows how the biggest term dominates. It remains a one-standard-deviation figure until a coverage factor is applied.
Combined standard uncertainty is 13 microns and the reference alone is 12 of it, buying a better probe won't help.
Also heard as
- combined uncertainty
- u_c
Related terms
Standard uncertainty
Uncertainty expressed as one standard deviation, the common currency for combining uncertainty components.
Law of propagation of uncertainty
The first-order formula that combines input standard uncertainties, weighted by sensitivity coefficients, into the output uncertainty.
RSS
Root sum of squares, combining independent uncertainty contributions by squaring, adding and taking the square root.
Expanded uncertainty
Combined standard uncertainty multiplied by a coverage factor to give an interval with a stated coverage probability.
Sensitivity coefficient
The factor that converts an input's uncertainty into its effect on the output, the partial derivative of the model.