Page 288 - Materials Chemistry, Second Edition

274 R.K. Rosenbaum et al.

Fig. 11.1 Illustrative comparison of impact scores from two options A and B with the point
estimates of 4 and 6, respectively, in all graphs, but with different uncertainties, low in the left,
high in the centre and mixed in the right graph

often hampered by the difficulty to assign and propagate uncertainty information of
the usually numerous parameters of a model as required by uncertainty assessment
methods. This problem becomes even more apparent when modelling large systems
as usually done in LCA, not to mention that there is more to overall uncertainty of a
model result than just what parameters contribute. In current daily LCA practice,
this often leads to complete omission of this important and integral aspect of any
model result, while it may potentially influence or even change the conclusions of a
study.
Uncertainty thus refers to everything we do not know and we cannot be certain
about, regardless whether we are aware of it or not. In order to create a common
basis of understanding when using technical terms and vocabulary around uncer-
tainty, a thorough definition of important terms and concepts will be provided as
starting point in the following section.

11.2 Essential Concepts and Definitions

In order to provide an accessible and operational angle on the subject, we have
deliberately chosen to use simplified terminology and explanations that do not
always capture everything there is to say. The focus of this chapter is on what is
relevant for LCA students and practitioners, not on covering all aspects around
statistical concepts, terms and definitions. For many concepts there may be multiple
terms that are used synonymously in literature and in some cases there may not
even be consensus on specific terms and their definition, such as what a sensitivity
analysis exactly is for example. The implicit imprecision may be shocking to
experts in statistics, but avoiding to capture the full complexity substantially helps
getting a first grasp and understanding of the main concepts and how they are used
in LCA practice, which is the main purpose of this chapter.