Statistical Calculation Guidelines
Statistical Calculations
For each measurement from a non-target instrument, the module calculates the following:
Observed Error
Observed Error = Result − Target
The raw difference between the instrument's measured value and the target value for that specimen. A positive value indicates the instrument reads higher than the target; negative indicates lower.
TEa (Total Allowable Error)
TEa = configured per analyte in Lab Settings (absolute or percentage); percentage TEa is applied at each specimen's target concentration
The maximum allowable difference between an instrument's result and the target, derived from the analyte's configured TEa and the bias allocation percentage. For percentage-based TEa, the allowable error is concentration-dependent — specimens at higher concentrations have proportionally wider absolute allowable error windows.
Error Index
Error Index = (Result − Target) / TEa
Normalizes the observed error by TEa, making performance directly comparable across specimens at different concentration levels. An Error Index magnitude ≤ 1.0 means the instrument's deviation falls within the allowable error window (PASS). A magnitude > 1.0 means it exceeds allowable error (FAIL). Target instruments are not assigned an Error Index — they are used only to establish the target value.
Coverage Ratio
Coverage = 100 × (Xhi − Xlo) / (Rhi − Rlo) where Xlo = max(min target value, lower AMR limit) and Xhi = min(max target value, upper AMR limit)
The percentage of the reportable range (AMR) spanned by the study's target values. A higher coverage ratio means the study evaluated inter-instrument agreement across a larger portion of the clinically relevant range. Low coverage ratios indicate that agreement was only assessed at a narrow band of concentrations, limiting confidence in extrapolating results across the full reportable range.