Page 134 - Design for Environment A Guide to Sustainable Product Development

Performance Indicators and Metrics 113

cycle cost reduction and a number of environmental performance met-
rics. Likewise, one can identify environmental improvement options
which may compromise other desirable features (e.g., recycled materi-
als may have poorer aesthetic qualities than virgin materials).
Aggregation and Scoring Schemes
A common practice in environmental performance measurement is
to use scoring or weighting techniques to aggregate together various
specific performance measures. For example, a frequently-used approach
to circumvent the challenges of environmental impact analysis is to
rely upon source measures but to assign them priorities or weights
based on an assessment of their relative importance, taking into
consideration the available information about environmental impact
pathways. Scoring schemes may be adopted to reflect a variety of dif-
ferent considerations, including
• Expectations of different stakeholder groups (e.g., customers
vs. community)
• Relative importance of environmental impacts (e.g., human
health vs. ecology)
• Internal business priorities (e.g., strategic advantage)

For example, the ISO 14040–43 guidelines for life-cycle assess-
ment include an intricate scheme for quantifying the impacts of sub-
stance emissions: classification of substances according to their effects
(e.g., carcinogens), characterization of their collective impacts based
on environmental exposure and effect modeling, normalization of the
effects relative to a benchmark, and weighting of effect scores based
on relative importance (see Chapter 9).
While the aggregation of performance metrics may be desirable
for purposes of simplifying decision making, there are a number of
problematic aspects to the use of scoring schemes for environmental
metrics:
• There are usually implicit policies and value judgments em -
bedded into the weighting system that are not apparent, yet
may skew the results in unintended ways.
• Performance metrics are much more meaningful when con-
sidered separately, whereas the significance of improvement
in an aggregated score is unclear.
• Aggregated measures can invite comparisons among dissim-
ilar products, facilities, or activities, while concealing impor-
tant differences between them.
By applying good practices, it is possible to avoid some of the
above abuses or pitfalls; for example, the traceability hierarchies used
in requirements management provide transparency for purposes of