Reducing uncertainty in LCI

Weidema B P, Frees N, Petersen E H, Øllgaard H (2003)

Publication info

Copenhagen: Danish Environmental Protection Agency. (Environmental project no. 862)


This report has been prepared with the aim of demonstrating how a data
collection strategy can be based on understanding the causes of variation in
the technological, geographical and temporal aspects of the processes included
in a life cycle assessment.

The objective of a data collection strategy is to prioritise the data collection so
that the necessary data is obtained in an adequate quality with the least effort.
Therefore, a natural target for the data collection strategy is to reduce the
overall uncertainty of the life cycle inventory to the level necessary to obtain a
result upon which conclusions can be based. Uncertainty, its causes, and ways
to reduce it, are therefore natural objects of interest when designing a data
collection strategy.

To reduce the overall uncertainty level of the life cycle inventory with the least
effort, the largest uncertainties should be reduced first, since these
uncertainties will dominate the overall uncertainty. However, some
uncertainties may be easily reducible, while others are irreducible. If the result
of a life cycle inventory is expected to be inconclusive at the level of the
irreducible uncertainties, it does not make sense to seek a reduction of
uncertainty at all, i.e. data collection should not be initiated. Chapter 2 deals
with procedures to identify and estimate the largest uncertainties in a life cycle
inventory. Chapter 3 introduces the distinction between reducible and
irreducible uncertainties, and combines the procedures of chapter 2 with
procedures to reduce uncertainties, arriving at an overall uncertainty-based
data collection strategy, which is summarized in section 3.7. The extensive
annex A reports the findings of an investigation into the causes of
technological, geographical and temporal variation in life cycle inventory data
from a number of industrial sectors. Annex B reports on the statistical
terminology applied.

This technical report is based on research performed from 1998 and up to the
end of 1999. It therefore does not include sources of information that have
become available after this date.

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