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and requirements are provided for Part 3: Scientific background 54 May 2001 calculating indicator results. Characterisation yields the ‘environmental profile’, consisting of a series of ‘indicator results’. Besides the mandatory elements there are three optional elements. The first of these, ‘Normalisation’, covers calculation of the magnitude of category indicators relative to reference information. In the second optional element, ‘Grouping of indicator results’, impact categories are grouped into one or more sets involving a descriptive sorting or a prioritising ranking. The third optional element is ‘Weighting’, i.e. multiplication of indicator results or normalised results by numerical factors, with the aim of converting and possibly aggregating indicator results across impact categories into a single score or a small number of such scores. As a final optional element, ‘Data quality analysis’ may be performed to enhance understanding of the significance, uncertainty and sensitivity of the LCIA results. The mandatory and optional steps described above imply that different trajectories can be adopted en route to the final LCIA result. These are illustrated in Figure 1.4.3.2. selection classification characterisation normalisation grouping weighting data quality analyis Figure 1.4.3.2: Options for combining mandatory and optional ISO LCIA steps. Part 3: Scientific background 55 May 2001 Based on ISO 14042, in this new Guide we distinguish the following steps of the Impact assessment phase: - [Procedures];1 - Selection of impact categories; - Selection of characterisation methods: category indicators, characterisation models and factors; - Classification; - Characterisation; - Normalisation; - Grouping; - Weighting. This structure is broadly similar to ISO 14042 (2000E). The main difference is that ‘Limitations of LCIA’ and ‘Comparative assertions disclosed to the public’ are not discussed here as separate steps of the LCIA phase. The limitations of LCIA are treated in the general introduction to this Guide, under Goal and scope definition and Interpretation: in the former, because the general limitations of LCA (including those of LCIA) should be duly appreciated before conducting the actual LCA study and in the latter because they put the conclusions into due perspective. Comparative assertions are one possible application of LCA; this is determined in the Goal and scope definition phase and will steer several choices during the LCA study (including the choice of simplified versus detailed LCA, application of weighting methods, reporting guidelines, etc.). Issues for Interpretation (covering the ISO topic ‘Data quality analysis’), reporting (covering ISO’s ‘Reporting’) and procedures (covering ISO’s ‘Critical review’) are treated in the same way as in Goal and scope definition (see Section 1.4). The selection of impact categories, category indicators and characterisation models has been broken down into two steps, moreover, because these are clearly sequential elements. Finally, this Guide does not entirely retain ISO’s distinction between mandatory and optional steps. The Dutch LCA community feels that normalisation and data quality assessment (issues for Interpretation) constitute at least recommended, if not mandatory, steps and that these should be part of any LCA study. The relation between the steps distinguished in this guide and the steps of ISO 14042 (2000E) is shown in Figure 1.4.3.3. 1 Parallel to the treatment of this subject in the Goal and scope phase, “Procedures” is a separate step in Part 2a - Guide - but not in Part 3 - Scientific background. Part 3: Scientific background 56 May 2001 Impact assessmentImpact assessment Selection of impact categories, category indicators and characterisation models Selection of impact categories Selection of characterisation methods: category indicators, characterisation models and factors Classification Classification Characterisation Characterisation Normalisation Normalisation Grouping Weighting Grouping Weighting Procedures Data quality analysis Limitations of LCIA Reporting and critical review Comparative assertions disclosed to the public This Guide ISO 14042 Figure 1.4.3.3: The relation between the Impact assessment steps distinguished in this Guide and in ISO 14042. Part 3: Scientific background 57 May 2001 1.4.4 Interpretation In ISO 14043 (2000E) the Interpretation phase is broken down into three elements: - Identification of significant issues, based on the results of the LCI and LCIA phases of LCA; - Evaluation, comprising completeness, sensitivity and consistency checks; - Conclusions, recommendations and reporting. Other elements of analysis, including a critical review, are considered additionally in clause 9 of ISO 14043. Based on ISO 14043, in this Guide we distinguish the following steps of the Interpretation phase: - [Procedures (Chapter 9 of ISO 14043)]1; - Evaluation of results: consistency check completeness check - Analysis of results: contribution analysis perturbation analysis sensitivity and uncertainty analysis - Conclusion and recommendations. This structure is broadly similar to ISO 14043. The main difference is that ‘Evaluation’ has been split into two parts, one of which is placed before ‘Identification of significant issues’. The reason for this change is that if there are large inconsistencies or errors in the data or if the data is very incomplete, all further Interpretation steps become futile. A minor difference is the use of the term analysis instead of check for the sensitivity and uncertainty analysis2. ‘Identification of significant issues’ is here operationalised in two different steps: the contribution analysis and the perturbation analysis. Reporting and procedures are treated in the same way as for the Goal and scope definition (see Section 1.4). For obvious reasons, and to prevent endless iteration, issues for Interpretation is no longer included as an item in the Interpretation phase itself. The relation between the steps distinguished in this guide and the steps of ISO 14043 (2000E) is shown in Figure 1.4.4.1. There is an close relationship between the steps of the Interpretation phase and the other phases of the LCA. On the one hand, there is input from the other phases, because these identify relevant issues for Interpretation. On the other hand, the iterative nature of the LCA process allows for, and sometimes even demands, making changes in prior phases, as when errors are found or results prove to be ‘too’ sensitive to particular, debatable data, model choices, etc. during Interpretation. 1 Parallel to the treatment of this subject in the Goal and scope phase, “Procedures” is a separate step in Part 2a - Guidelines - but not in Part 3 - Scientific background. 2 Here, the term check is used to emphasise the fact that data or model choices are being checked, while the term analysis is used for more complex assessments requiring dedicated tools and so on. Part 3: Scientific background 58 May 2001 InterpretationInterpretation Evaluation by -completeness check -sensitivity check -consistency check -other checks Consistency check Completeness check Contribution analysis Identification of significant issuesPerturbation analysis Conclusions, recommendations and reporting Sensitivity and uncertainty analysis Conclusions and recommendations This Guide ISO 14043 Procedures Evaluation of results Analysis of results Conclusions and recommendations Figure 1.4.4.1: The relation between the Interpretation steps distinguished in this Guide and in ISO 14043. 1.5 Further reading guidance In the following chapters the steps distinguished above are discussed for each phase of LCA, viz. Goal and scope definition, Inventory analysis, Impact assessment and Interpretation. Each step is discussed according to a fixed format: ‘Topic’, ‘Developments