QUALITY ASSURANCE & LAB ACCREDITATION

Transcription

1 TOP 9 QUALITY ASSURANCE & LAB ACCREDITATION Control Charts Accreditation of laboratories 6./7.Dec 2011 Workshop ANKARA TOP 9 Quality 1

2 TOP 9 QUALITY ASSURANCE & LAB ACCREDITATION Control Charts Accreditation of laboratories 6./7.Dec 2011 Workshop ANKARA TOP 9 Quality 2

3 Trueness and precision - systematic and stochastic errors 3

4 Terms related to precision Trueness = accuracy = accuracy of the mean Precision Repeatability - within laboratory - short term Intermediate precision - within laboratory long term Reproducibility - between laboratories The objective is to produce results which are true and precise 4

5 Topic Trueness = accuracy Precision Repeatability Intermediate precision Reproducibility information about: systematic error stochastic errors precision of 1 sample, 1 lab technician, 1 analyzer, identical reagents, same day standard situation mean of 2 4 results precision of 1 sample, however more variations within lab e.g. control chart 1 sample, >2 tester, >2 laboratories 5

6 Control chart Principal tool for internal quality control Analyse a number of routine samples and control samples Normally one control value for each batch is entered to the control chart most common: X-charts control-limits: statistical standard deviation central line: mean value 6

7 Control Chart previous period parameter: Lead (Pb) matrix: Grassmeal Date mg/kg 1 1,07 2 0,89 3 0,94 4 0,92 5 0,87 6 1,10 7 0,97 m g/kg 1,50 1,30 1,10 0,90 Parameter: Pb Control Chart Matrix: Grassmeal 20 0,88 mean 0,9620 standard deviation 0,0873 2*std dev. 0,1747 3*std dev. 0,2620 Limits lower warning limit 0,7873 upper warning limit 1,1367 lower control limit 0,7000 upper control limit 1,2240 0,70 0, Date of analysis 7

8 Control limits 1,50 Parameter: Pb Control Chart Matrix: Grassmeal 1,30 upper control limit +3 s mg/kg 1,10 0,90 upper warning limit + 2 s mean lower warning limit - 2s 0,70 lower control limit - 3s 0, Date of analysis 8

9 Daily interpretation There are 3 possible cases: 1) The method is in control 2) The method is in control but the long-term evaluation shows that the method is out of statistical control 3) The method is out of control 9

10 In-control-situation Control Chart parameter: Pb matrix: Grassmeal 1,50 1,30 1,10 mg/kg 0,90 0,70 0, Date of analysis The control value is within the warning limits: the analyst can report the analytical results no further reactions 10

11 Control Chart parameter: Pb matrix: Grassmeal 1,50 1,30 1,10 mg/kg 0,90 0,70 0, Date of analysis 11

12 Control Chart parameter: Pb matrix: Grassmeal 1,50 1,30 mg/kg 1,10 0,90 0,70 0,50 out of control rule: two out of three > 2 s Date of analysis 12

13 Reaction, when out of control-situation Normally no analytical results can be reported All result since last value in control was obtained must be reanalysed 13

14 Control Chart parameter: Pb matrix: Grassmeal 1,50 1,30 out of statistical control 7 * ascendend mg/kg 1,10 0,90 0,70 0, Date of analysis 14

15 Control Chart parameter: Pb matrix: Grassmeal 1,50 1,30 out of statistical control 7 * descendend 1,10 mg/kg 0,90 0,70 0, Date of analysis 15

16 Control Chart parameter: Pb matrix: Grassmeal 1,50 1,30 out of statistical control 10 * above the mean value 1,10 mg/kg 0,90 0,70 0, Date of analysis Note: Other recommendations: 7 * above the mean value 16

17 Control Chart parameter: Pb matrix: Grassmeal 1,50 1,30 out of statistical control 10 * below mean value 1,10 mg/kg 0,90 0,70 0, Date of analysis 17

18 Reaction, when out of statistical control The analyst can report the analytical results But a problem may be developing Discover important trends as early as possible to avoid serious problems Each laboratory has to decide in the quality manual how to give attention to these trends generate standard operation procedures (SOPs) 18

19 Types of control charts X-Chart accuracy, central line = mean-value possible in X-Charts: Range chart repeatability central line = nominal value (CRM) relativ differences between duplicate analyzes Blank value chart contamination of reagents Recovery chart recovery, central line = 100 % 19

20 TOP 9 QUALITY ASSURANCE & LAB ACCREDITATION Control Charts Any Questions? 6./7.Dec 2011 Workshop ANKARA TOP 9 Quality 20