Microsoft PowerPoint - Introduction to Equivalence-print version.ppt

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					                                        Introduction to Equivalence

                                                           Pascual Pérez Ballesta

                                                    Transport and Air Quality Unit
                                         Institute for Environment and Sustainability (IES)
                                                              Ispra, Italy
                                                              http://ies.jrc.cec.eu.int
                                                             http://www.jrc.cec.eu.int




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                              Structure of the Workshop
                                                                      Legislation
                            CURRENT STATE OF THE ART                  Standardisation
                                                                      Harmonisation
                Chair: Peter Woods (NPL, UK),                         Certification &
                Rapporteurs: U. Pfeffer (LANUV, NRW, D)
                                                                        type approval
                                 FOCUSING ON THE ISSUE                Implementation
                                                                      -----------------------
                Chair: P. Quincey (NPL, UK) ,                         Statistical treatment
                Rapporteurs: A. Borowiak (DG-JRC)
                                                                      PM equivalence
                 EXPERIENCES IN DIFFERENT MEMBER                      Practical cases:
                              STATES                                   local and national
                                                                       experiences
                Chair: T. Hafkenscheid (NMi, NL),
                Rapporteurs: M. Froehlich (Umweltbundesamt GmbH, A)   -----------------------
                                         OPEN DISCUSSION              Future actions

                Chair: T. Hafkenscheid (NMi, NL)

Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                              Comparison
                            of Air Quality
                                 Data




                                                           A procedure of
                                                           equivalence is more
                                                           than a further step
                                                           in the process of
                                                           data comparison



Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
            IMPROVEMENT OF AIR QUALITY DATA



            On the assumption that data are generated
            by the reference method defined by the EC
            directives.




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                 Reduce the uncertainty of the reference material



                                  Reduce the uncertainty of the reference method



                                                 MEET THE UNCERTAINTY
                                                  REQUESTED BY THE EC
                                                DATA QUALITY OBJECTIVES




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                  Legislative actions for improvement
                                   of the sampling representativeness



                      • Network design: macro and micro criteria
                      • Data capture and time coverage
                      • Reference periods




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                      Working programs and other
                                     regulations for improvement
                                       of the analytical technique



                             • Standardisation
                             • Intercomparison and proficiency testing
                             • Type approval of instruments




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                    The use of equivalence methods bears a series of
                  significant legal, economic and technical implications

             • DATA with the same legal value of the reference method


            • Market-driven and low cost monitoring


             • Different measurement strategies




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                                      EQUIVALENCE METHOD


                                        ON BY-PASSING
                              SOME QAQC PROCEDURES IMPLEMENTED
                                  FOR THE REFERENCE METHOD

                  REPORTING LOWER QUALITY DATA




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                                   EQUIVALENCE METHOD

                      …..a method that meets the EC Data Quality Objectives




                                    …..meets the same uncertainty criteria
                                          of the reference method




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                               EQUIVALENCE PROCEDURE
              Option A:

                       Full validation of the method, determination of the measurement
                       uncertainty of the candidate method according to GUM.


              Option B:

                       Side by side comparison with a reference method under field
                       conditions



Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                  Overall uncertainty evaluation

                       Laboratory and field test according to grade of
                       variation

                        Separate analysis of uncertainty budgets

                        Good estimation of the method’s uncertainty

                         Final test under field conditions


Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                  Overall uncertainty evaluation



                         High cost associated to a complete evaluation

                         Not always applicable to all the methods




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                               Side by side comparison

                    Reference value is determined by the reference
                    method

                    Correction factors can be used “if consistent”

                    The validation range of ambient conditions are
                    defined by the local conditions during the field test


Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                               Side by side comparison

                   Possible influence of the reference method’s
                   uncertainty on the test result

                   How to deal with outliers

                   How to deal with correction factors

                   Generalisation of the equivalence test

Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                          U CM ≠ f (U RM)

               Transitive property
                     Uncertainty of the
                     reference method                      >
                                             Uncertainty of the
                                              candidate method
                     X         an overestimation of the UCM




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                          U CM ≠ f (U RM)

               Transitive property

                                                           <
                      Uncertainty of the                       Uncertainty of the
                      reference method                         candidate method
                     X                an underestimation of the UCM



Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                          U CM ≠ f (U RM)

               Transitive property

                                   If       CMa ↔ RM and      CMb ↔ CMa

                                            Then
                                                           CMb ↔ RM




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                               Side by side comparison

                   Possible influence of the reference method’s
                   uncertainty on the test result

                   How to deal with outliers

                   How to deal with correction factors

                   Generalisation of the equivalence test

Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                                            Quantification
                                                            of a compound

                                                               measure


                                                           physical property,
                                                           which is related
                                                           to concentration

                        The measured property may be affected by external variables

                         Different methods can measure different properties



Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                                      Corollaries
                  Different methods that measure different properties
                  show different behaviours to environmental variables

                 The measured property is not stable or is affected by
                 measurement conditions

             Equivalence is defined for local situations and
             under limited conditions of sampling



Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                               PRACTICAL IMPLICATIONS
                If the study is not accompanied with an in-depth understanding of the
                effect of the environmental variables on the measurement capability
                of the method and a de-limitation of the validation range, the application
                of a general protocol may lead to misinterpretation.

               Equivalence should be defined by the national competence authority
               on the basis of the validation study and location.


               Recognition of equivalence methods between EU members cannot be
               automatic.



Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007
                                                           To Start….

                “…and between these two inaccuracies there is this
               uncertainty relation.”


                             “The Development of the Uncertainty Principle” M. Heisenberg, 1976.




Workshop on Demonstration of Equivalence for ambient air
monitoring methods. Ispra 2-4 May 2007