Reducing Uncertainty in LCI

Reducing Uncertainty in LCI

1 Introduction

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.