Quality parameters estimation

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Quality Control data evaluation & comparision using Classical & Robust statistics - Courtesy FICCI

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Quality parameters estimation

  1. 1. QUALITY PARAMETERS USING CLASSICAL & ROBUST STATISTICS FICCI QUALITY FORUM 1 Training on assuring quality of test results
  2. 2. Internal Quality Control (IQC) is continuous and immediate monitoring of quality of test result by laboratory personnel External Quality Assessment (EQA) refers to a system in which the quality of test result is assessed periodically and retrospectively by an independent outside agency FICCI QUALITY FORUM 2 Training on assuring quality of test results
  3. 3. DIFFERENT IQC TECHNIQUES  Coefficient of Variation (% CV) with Controls (should be less than 5 %)  ‘Z’ score ( 3  L & J Charts  Within Lab ‘Z’ score (3  Between Lab ‘Z’ score (3 FICCI QUALITY FORUM Z 2) 3 ZW 2) ZB 2) Training on assuring quality of test results
  4. 4. COEFFICIENT OF VARIATION (CV) (Classical) It describes the standard deviation as a percentage of the mean n-1 CV = ------- x 100 FICCI QUALITY FORUM 4 Training on assuring quality of test results
  5. 5. Coefficient of Variation, CV is a measure of precision of the test data Lower the CV, more precise is the data In most laboratory testing, the CV should be less than 5% for analytical measurement FICCI QUALITY FORUM 5 Training on assuring quality of test results
  6. 6. EXAMPLE - 10 The run of a Reference Material over few days gave the following data 5.74, 5.55, 5.70, 5.01, 5.48, 5.83, 5.81, 5.78, 5.71, 4.66, 5.56, 5.64, 5.66, 5.75 g/kg To Estimate CV (classical) Average = 5.563 g/kg Std. Dev. = 0.332 g/kg % CV (Classical) = 100 * (0.332 / 5.563) = 5.96 % FICCI QUALITY FORUM 6 Training on assuring quality of test results
  7. 7. Z - Score : It is a normalized value which gives a score to each result relative to other members in the group, such that Z=0 means that the result agrees well with others Result – Mean XClassical Z-Score = ------------------------ = -------Sample Std Dev n-1 FICCI QUALITY FORUM 7 Training on assuring quality of test results
  8. 8. Z - SCORE VALUES – ISO GUIDE 43 LESS THAN BETWEEN MORE THAN FICCI QUALITY FORUM 2 2 & 3 = SATISFACTORY 3 = QUESTIONABLE = 8 UNSATISFACTORY Training on assuring quality of test results
  9. 9. Z - SCORE IS UNITLESS A positive ‘z’ score means that the value is above the mean A negative score means that the value is below the mean FICCI QUALITY FORUM 9 Training on assuring quality of test results
  10. 10. EXAMPLE - 11 In the Example - 10, to estimate ‘Z’ score at 5.48 g/kg The data are 5.74, 5.55, 5.70, 5.01, 5.48, 5.83, 5.81, 5.78, 5.71, 4.66, 5.56, 5.64, 5.66, 5.75 g/kg Average ( ) = 5.563 g/kg Std. Dev. ( n-1 ) = 0.332 g/kg 5.48 - 5.563 Classical Z5.48 = ----------------- = - 0.25 0.332 FICCI QUALITY FORUM 10 Training on assuring quality of test results
  11. 11. PROFICIENCY OF CALIBRATION LABORATORY AS PER ISO GUIDE 43:1997 (Lab – Ref) EN = --------------------(U2Lab + U2Ref) where, Lab = Participating laboratory’s result Ref = Reference laboratory’s result ULab = Participating laboratory’s uncertainty Uref = Reference laboratory’s uncertainty FICCI QUALITY FORUM 11 Training on assuring quality of test results
  12. 12. EN = Error normalized An En number in the range of –1 to +1 indicates that the laboratory value and the reference value agree with each other within their respective uncertainties and is considered a success. FICCI QUALITY FORUM 12 Training on assuring quality of test results
  13. 13. CALCULATION OF EN VALUE EXAMPLE - 12 DATA GIVEN ARE : Sl. No. Pr. Gauge Rd. (Bar) Value MU Value MU 1 4.0 3.999 0.020 4.00043 0.0057 2 10.0 10.004 0.023 10.00207 0.0058 FICCI QUALITY FORUM Lab. Cal. 13 Ref. Cal. Training on assuring quality of test results
  14. 14. EN (4.0) (3.999 – 4.00043) = ----------------------------[(0.020)2 + (0.0057)2] = - 0.069 EN (10.0) (10.004 – 10.00207) = ----------------------------[(0.023)2 + (0.0058)2] = 0.081 FICCI QUALITY FORUM 14 Training on assuring quality of test results
  15. 15. COEFFICIENT (Robust) OF VARIATION (CV) 0.7413* IQR CV = ------------------ x 100 Median Where IQR = Inter Quartile Range FICCI QUALITY FORUM 15 Training on assuring quality of test results
  16. 16. EXAMPLE - 13 To Estimate CV (robust) of the data given in Example – 10. 5.74, 5.55, 5.70, 5.01, 5.48, 5.83, 5.81, 5.78, 5.71, 4.66, 5.56, 5.64, 5.66, 5.75 g/kg Reorganizing of the data and the solution is given on the next slide. FICCI QUALITY FORUM 16 Training on assuring quality of test results
  17. 17. Sl. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 FICCI QUALITY FORUM Data 5.74 5.55 5.70 5.01 5.48 5.83 5.81 5.78 5.71 4.66 5.56 5.64 5.66 5.75 Sorted Data 4.66 5.01 5.48 5.55 5.56 5.64 5.66 5.70 5.71 5.74 5.75 5.78 5.81 5.83 Q1 = Q2 = Q3 = IQR = NIQR = 5.55 5.68 5.75 0.20 0.148 Unit of above data is g/kg 0.148 Robust CV = --------- x 100 5.58 = 2.61 % 17 Training on assuring quality of test results
  18. 18. Result – Median Robust Z-Score = -----------------------NIQR In the Example - 10, to estimate Robust ‘Z’ score at 5.48 The data are 5.74, 5.55, 5.70, 5.01, 5.48, 5.83, 5.81, 5.78, 5.71, 4.66, 5.56, 5.64, 5.66, 5.75 g/kg FICCI QUALITY FORUM 18 Training on assuring quality of test results
  19. 19. Example - 14 In the Example - 10, to estimate Robust ‘Z’ score at 5.48 g/kg. The data are 5.74, 5.55, 5.70, 5.01, 5.48, 5.83, 5.81, 5.78, 5.71, 4.66, 5.56, 5.64, 5.66, 5.75 g/kg Already calculated, Median = 5.66 g/kg & NIQR = 0.2 g/kg 5.48 - 5.66 Robust Z5.48 = ----------------- = - 1.35 0.2 FICCI QUALITY FORUM 19 Training on assuring quality of test results
  20. 20. The data of Example - 10 5.74, 5.55, 5.70, 5.01, 5.48, 5.83, 5.81, 5.78, 5.71, 4.66, 5.56, 5.64, 5.66, 5.75 g/kg Type of Statistics Z5.48 Classical Statistics 5.96 % - 0.25 Robust Statistics FICCI QUALITY FORUM CV 2.61 % - 1.35 20 Training on assuring quality of test results
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