The requirement for congruence in normalisation

Two purposes for normalization in LCA are presented: resolving non-commensurate units, and assessing significance. Two families of approach for normalization in LCA are described: internal and external. The need for congruence between the normalization and valuation is illustrated by showing the nonsensical conclusions which can result from an approach that is common in North American LCA applications: internal normalization with external valuation. In order to achieve congruence with internal normalization methods, valuation in such instances must be case-specific. External normalization methods bring an added benefit not provided by internal normalization methods: an assessment of relative significance.