1 Exercise 7: Accuracy and precision

2 Origin of the error : Accuracy and precision Systematic (not random) –bias –impossible to be corrected  accuracy Random –can be evaluated by statistics  precision

3 Good Precision Good Accuracy Poor Precision Good Accuracy Good Precision Poor Accuracy Poor Precision Poor Accuracy Gold Standard Silver Standard Off-Base Model Hit or Miss Model Bias and precision

4 Accuracy Closeness of determined value to the true value. The acceptance criteria is mean value  15% deviation from true value. At LOQ, 20% deviation is acceptable.

5 The accuracy is calculated using the following equation : The accuracy at each concentration level must be lower than 15% except a LOQ (20%) Accuracy

6 Determination –by replicate analysis of the sample containing known amount of analyte –5 samples for at least 3 levels –The mean value should be within 15% of the actual value except at LOQ where it should not deviate by more than 20%

7 Precision T he closeness of replicate determinations of a sample by an assay. The acceptance criteria is  15% CV. At LOQ, 20% deviation is acceptable.

8 Repeatability (r) Agreement between successive measurements on the same sample under the same conditions Reproducibility (R) The closeness of agreement between results obtained with the same method under different conditions Precision

9 Precision… Considered at 3 Levels Repeatability Intermediate Precision Reproducibility

10 Repeatability Express the precision under the same operating conditions over a short interval of time. Also referred to as Intra-assay precision –(within day)

11 Intermediate Precision Between-run, between day repeatability … also named intermediate precision, which measures precision with time (often days) and may involve different analysts, equipment, reagents…

12 Precision: measurement Should be measured using a minimum of 5 determinations per concentration –A minimum of 3 concentrations in the range of expected concentrations –The precision at each concentration should not exceed 15% except for the LOQ (20%)

13 Raw data

14 Precision: measurement for a single measurement : CV(%) for intra-day and inter-day precision  ANOVA

15 Variance of intermediate precision

16 Estimation of the two components of the variance we need a proper statistical model that is the one-way nested analysis of variance model given as : With i=1,2..n days and j=1,2,…replicates; in this equation, Y ij are observed values, μ is the true value of the common stock solution being assayed in this experiment, b i is a random component for between-days variation and w ij is another random component for within-day variation. The variance of b i is and the variance of w ij is.

17 ANOVA Allows an estimation of the 2 variance terms –inter-day mean square (BMS) –intra-day mean square (WMS)

18 The exercise consist to compute these variances By hand Using an ANOVA (Excel) With Analyse- it

19 The limit of quantification (LOQ) LOQ is the lowest amount of analytes in a sample which can be determined with defined precision and accuracy LOQ :  20%

20 Limit of quantification (LOQ) The lowest standard on the calibration curve is the LOQ if: –no interference is present in the blanks at retention time of the analyte for this concentration –the response (analyte peak) has a precision of 20% and accuracy %

21 Three analytical areas 1 23 XbXb not detected Area of detection Area of quantification or CV<20% LODLOQ