Secondary data is data obtained from sources other than direct measurement or collection from the specific activity or process being studied in a Life Cycle Assessment. This type of data typically comes from existing databases, published literature, industry averages, or previously conducted studies rather than from direct observation or measurement of the particular system under investigation.
ISO 14044 addresses data quality requirements and acknowledges that LCA practitioners often need to combine different types of data sources. Secondary data serves as an essential complement to primary data, particularly when direct measurement is impractical, too costly, or when studying activities outside the practitioner's direct control or geographical reach.
Common sources of secondary data in LCA include commercial and public LCA databases such as ecoinvent, Bonsai, GaBi, or ELCD, industry association reports, government statistics, scientific publications, and generic process data. Whilst secondary data provides broader coverage and allows for more complete life cycle modelling, it inherently carries greater uncertainty than primary data because it represents average or generic conditions rather than the specific characteristics of the system being studied.
The distinction between secondary and primary data is crucial for data quality assessment and uncertainty analysis in LCA. ISO 14044 requires that data quality be evaluated based on criteria including technological, geographical, and temporal representativeness. Secondary data typically scores lower on these representativeness criteria when applied to specific systems, though it may be entirely appropriate for background processes or when system-specific data is unavailable.
