Page 363 - Materials Chemistry, Second Edition

5.6 Illustration of the Component Interpretation Using an Example of Practice 347

5.6.5
Significance of Differences
Since an over-interpretation of differences between compared product systems
must be avoided, the examination of their significance is central to the reliability of
an LCA study.

According to ISO 14042 (new ISO 14044), depending on the definition of goal
and scope, information and procedures that allow a deduction of significant
results may become necessary. This applies, if, as in the present case, LCA
results may be part of market-strategic or political decision-making.
Since an examination of significance on the basis of error computation
with error propagation in a strict mathematical sense is regarded critically
owing to the data structure in LCAs, the following references are meant to
provide an orientation as to when differences between systems are to be
regarded as relevant.
The dominance analysis (sectoral analysis) represented in Section 4.1 may
be regarded as an important support. It was stated that for PET bottles,
substantial impacts are mainly caused by the supply of the bottle material.
Indicator results of the beverage carton systems are affected by several
sectors. Particularly relevant is the production of the individual composite
materials, namely, aluminium, polyethylene and raw cardboard, as well as
the production of closures.
During the project processing, there was particular emphasis on the
quality of data and assumptions in these sectors (see also Chapters 2 and 3).
The remaining uncertainties regarding PET bottle weights were examined by
sensitivity analyses.
The practitioners express the opinion that the data and assumptions used
are applicable for the result-relevant sectors of the examined packaging
systems and that they are, to a large extent, symmetrical in actuality. On
this basis, the results can be regarded as sound and robust. Uncertainties
concerning the accuracy and representativeness of the data such as those
discussed are nevertheless inevitable to a certain extent. Consequently, small
differences of indicator values for a comparison of packaging systems are
less significant than larger ones.
Even if discrete declarations for significance thresholds in LCA studies
cannot be reliably deduced, as a result of basic objections, a system com-
parison of the beverage carton and PET packagings was nevertheless made
by using a significance threshold in order to avoid an over-interpretation of
small differences.
The Institut f¨ ur Energie und Umweltforschung (IFEU) usually applies a
significance threshold value of 10% for the analysis of packaging systems.
This is a pragmatic and common approach in LCA praxis and regarded