GIFSQ Tools · Module 15 — Metrology, Validation & Laboratory Accreditation · Tool 284 of 500
Test the linearity of a method across its working range: fit the line through level means, find the largest residual as a percentage of nominal, and check the fit.
Try sample values — fills the form with the worked example below.
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Slope
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Intercept
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R²
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Largest residual (%)
Equation: Least-squares line ŷ = a + bx (same formulas as the calibration curve). Residual at level i = (yᵢ − ŷᵢ) ÷ xᵢ × 100%. Largest residual = the maximum absolute residual across levels.
Method: Linearity assessment per ICH Q2(R2) and Eurachem method-validation guidance: at least 5 levels spanning the range, each measured in replicate, with residuals expressed against the nominal level.
Assumptions: the nominal levels are exact; the measured means are unbiased estimates at each level; residuals are independent across levels.
Limitations: a high R² can hide a curved pattern — always inspect the residual sign pattern; a single outlying level can dominate the largest residual, so confirm it with a repeat before rejecting the range.
Rounding: slope and intercept to 4 decimal places; R² to 4 decimal places; largest residual to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Linearity assessment per ICH Q2(R2) and Eurachem method-validation guidance: at least 5 levels spanning the range, each measured in replicate, with residuals expressed against the nominal level.
Assumptions: the nominal levels are exact; the measured means are unbiased estimates at each level; residuals are independent across levels.
Limitations: a high R² can hide a curved pattern — always inspect the residual sign pattern; a single outlying level can dominate the largest residual, so confirm it with a repeat before rejecting the range.
Rounding: slope and intercept to 4 decimal places; R² to 4 decimal places; largest residual to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Levels 1, 2, 3, 4, 5 mg/L with means 1.02, 1.98, 3.05, 3.96, 5.01: slope = 0.9960, intercept = 0.0160, R² = 0.9995, largest residual = 1.53% at the 3 mg/L level.
Enter values above to see results.
Many methods accept linearity when the largest residual stays within ±5% of nominal and R² is 0.99 or better — use your own method criterion. Tool 284 of 500 — GIFSQ
