GIFSQ Tools · Module 4 — Microbiology Methods & Laboratory Operations · Tool 72 of 500
Compare an alternative microbiology method against a reference method on paired samples: bias, 95 % confidence interval of the difference, and equivalence against the 0.5 log limit.
Try sample values — fills the form with the worked example below.
–
Bias (alternative − reference), log10
–
95 % CI half-width, log10
–
Equivalent within 0.5 log
Equation: Bias = mean(alternative) − mean(reference). Standard error SE = s ÷ √n, where s is the standard deviation of the paired differences and n is the number of pairs. 95 % confidence interval = bias ± 1.96 × SE. Equivalence when |bias| + 1.96 × SE ≤ 0.5 log10.
Method: ISO 16140-2, validation of alternative (proprietary) methods against a reference method — paired-sample comparison with a 0.5 log10 equivalence limit for quantitative methods.
Assumptions: the paired differences are approximately normally distributed; the pairs are independent; both methods were run on the same samples under the same conditions.
Limitations: equivalence here is a statistical screen, not full ISO 16140-2 validation, which also requires inclusivity, exclusivity, sensitivity and relative-level studies. A small n gives a wide interval and can fail equivalence even for an unbiased method.
Rounding: bias, standard error and confidence limits to 3 decimal places. The 0.5 log10 limit is applied to the unrounded values.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: ISO 16140-2, validation of alternative (proprietary) methods against a reference method — paired-sample comparison with a 0.5 log10 equivalence limit for quantitative methods.
Assumptions: the paired differences are approximately normally distributed; the pairs are independent; both methods were run on the same samples under the same conditions.
Limitations: equivalence here is a statistical screen, not full ISO 16140-2 validation, which also requires inclusivity, exclusivity, sensitivity and relative-level studies. A small n gives a wide interval and can fail equivalence even for an unbiased method.
Rounding: bias, standard error and confidence limits to 3 decimal places. The 0.5 log10 limit is applied to the unrounded values.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Reference mean 4.20 log10 CFU/g, alternative mean 4.32, standard deviation of the differences 0.25, n = 25 pairs. Bias = 0.120 log10; SE = 0.25 ÷ 5 = 0.050; 95 % CI = 0.022 to 0.218; |bias| + half-width = 0.218, within 0.5 log10, so the methods are equivalent.
Enter values above to see results.
ISO 16140-2 uses a 0.5 log10 accuracy limit for quantitative alternative methods. Report the bias and its interval, not the bias alone — a small bias with a wide interval is not proven equivalent. Tool 72 of 500 — GIFSQ
