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# Within & between lab z scores

## by National Institute of Biologicals on Oct 24, 2013

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## Within & between lab z scoresPresentation Transcript

• WITHIN LAB & BETWEEN LAB Z - SCORES FICCI QUALITY FORUM 1 Training on assuring quality of test results
• Within & Between Lab Z-scores are calculated from normalised difference and normalised sum of two sets of data If ‘A’ & ‘B’ are the two sets of replicate data, then Normalised difference, D = (A-B) / 2 if A>B D = (B-A) / 2 if A<B Normalised sum, S = (A+B) / 2 FICCI QUALITY FORUM 2 Training on assuring quality of test results
• WITHIN LAB ‘Z’ SCORE The normalized difference reflects a laboratory’s ability to reproduce exactly the same result, and can be considered an estimate of precision. This Z score is called the ‘within’ laboratory Z score or ZW (D - Median ‘D’) ZW = ---------------------NIQR (D) FICCI QUALITY FORUM 3 Training on assuring quality of test results
• Precision of routine work can be monitored by estimating within lab ‘Z’ score      Perform tests on 11 replicate samples, one portion being ‘A’ and the other portion being ‘B’, from the same product Estimate the normalized difference ‘D’ Find median of ‘D’ and NIQR of ‘D’ Estimate within lab ‘Z’ score ‘ZW’ as ZW = (D-Median 'D') / NIQR (D) Thereafter rearrange ZW values as per Sample Sl. No. for ease of understanding FICCI QUALITY FORUM 4 Training on assuring quality of test results
• E x a m p l e Sl No Sample A Sample B Diff, D=(A-B)/ 2 1 8.25 8.22 0.0212 2 3 4 5 6 8.13 8.22 8.14 7.98 8.30 8.28 8.24 8.17 8.08 8.14 -0.1061 -0.0141 -0.0212 -0.0707 0.1131 15 7 8 9 10 11 8.20 8.01 7.96 8.24 8.16 8.27 8.06 8.09 8.09 8.12 -0.0495 -0.0354 -0.0919 0.1061 0.0283 Here, Median A = 8.16 & Median B = 8.14 FICCI QUALITY FORUM 5 Training on assuring quality of test results
• Rearranged data ‘D’ -0.1061 -0.0919 -0.0707 -0.0495 -0.0354 -0.0212 -0.0141 0.0212 0.0283 0.1061 0.1131 FICCI QUALITY FORUM IQR & NIQR Quartiles Q1 = -0.0707 IQR = 0.0990 Q2 = -0.0212 NIQR =0.0734 Q3 = 0.0283 6 ZW -0.857 -0.714 -0.500 -0.286 -0.143 0.000 0.071 0.428 0.500 1.286 1.357 Training on assuring quality of test results
• ZW AS PER SAMPLE SL. NO. SL NO SAMPLE A SAMPLE B ZW 1 2 3 8.25 8.13 8.22 8.22 8.28 8.24 0.43 -0.86 4 8.14 8.17 0.00 5 7.98 8.08 -0.50 6 7 8 8.30 8.20 8.14 8.27 1.36 -0.29 8.01 8.06 -0.14 9 7.96 8.09 -0.71 10 8.24 8.09 11 8.16 8.12 1.29 0.50 FICCI QUALITY FORUM 7 0.07 Training on assuring quality of test results
• WITHIN LAB ‘Z’ SCORE Here all the ZW values are within 2. Therefore, the Lab may be considered to have good precision FICCI QUALITY FORUM 8 Training on assuring quality of test results
• BETWEEN LAB ‘Z’ SCORE The normalized sum demonstrates a laboratory’s bias in its results due to equipment, operator or test methods. This Z score is called the ‘between’ laboratory Z score or ZB (S - Median ‘S‘) ZB = ---------------------NIQR (S) FICCI QUALITY FORUM 9 Training on assuring quality of test results
• Laboratory bias of routine work can be estimated from the data of replicate tests      Perform tests on 11 replicate samples, one portion being ‘A’ and the other portion being ‘B’, from the same product Estimate the normalized sum ‘S’ Find median of ‘S’ and NIQR of ‘S’ Estimate between lab ‘Z’ score ‘ZB’ as ZB = (S-Median ‘S') / NIQR (S) Thereafter rearrange ZB values as per Sample Sl. No. for ease of understanding FICCI QUALITY FORUM 10 Training on assuring quality of test results
• E x a m p l e Sl No Sample A Sample B Sum, S=(A+B)/ 2 1 8.25 8.22 11.646 2 3 4 8.13 8.22 8.14 8.28 8.24 8.17 11.604 11.639 11.533 5 7.98 8.08 11.356 6 8.30 8.14 11.625 16 7 8 9 8.20 8.01 7.96 8.27 8.06 8.09 11.646 11.363 11.349 10 11 8.24 8.16 8.09 8.12 11.547 11.512 FICCI QUALITY FORUM 11 Training on assuring quality of test results
• Rearranged data ‘S’ 11.349 11.356 11.363 11.512 11.533 11.547 11.604 11.625 11.639 11.646 11.646 FICCI QUALITY FORUM IQR & NIQR Quartiles Q1 = 11.363 IQR = 0.276 Q2 = 11.547 NIQR =0.2045 Q3 = 11.639 12 ZB -0.97 -0.93 -0.90 -0.17 -0.07 0.00 0.38 0.28 0.45 0.48 0.48 Training on assuring quality of test results
• ZB AS PER SAMPLE SL. NO. SL NO SAMPLE A SAMPLE B ZB 1 2 3 4 5 6 7 8 9 10 11 8.25 8.13 8.22 8.14 7.98 8.30 8.20 8.01 7.96 8.24 8.16 8.22 8.28 8.24 8.17 8.08 8.14 8.27 8.06 8.09 8.09 8.12 0.48 0.28 0.45 -0.07 -0.93 0.38 0.48 -0.90 -0.97 0.00 -0.17 FICCI QUALITY FORUM 13 Training on assuring quality of test results
• BETWEEN LAB ‘Z’ SCORE Here all the ZB values are within 2. Therefore, the Lab may be considered to have good bias or accuracy. FICCI QUALITY FORUM 14 Training on assuring quality of test results
• EXAMPLE OF ZW & ZB SL NO SAMPLE A 1 2 3 4 5 6 7 8 9 10 11 FICCI QUALITY FORUM 8.25 8.13 8.22 8.14 7.98 8.30 8.20 8.01 7.96 8.24 8.16 SAMPLE B ZW ZB 8.22 8.28 8.24 8.17 8.08 8.14 8.27 8.06 8.09 8.09 8.12 0.43 -0.86 0.07 0.00 -0.50 1.36 -0.29 -0.14 -0.71 1.29 0.50 0.48 0.38 0.45 -0.07 -0.93 0.28 0.48 -0.90 -0.97 0.00 -0.17 15 Training on assuring quality of test results