UNFCCC Definition:

Consistency means that an inventory should be internally consistent in all its elements over a period of years. An inventory is consistent if the same methodologies are used for the base and all subsequent years and if consistent data sets are used to estimate emissions or removals from sources or sinks. Under certain circumstances an inventory using different methodologies for different years can be considered to be consistent if it has been recalculated in a transparent manner taking into account any good practices.

Statistical Definition:

A statistical estimator for a parameter is said to be consistent, if the estimator tends towards the parameter as the size of the sample used for the estimator increases (i.e., precision is improved by an increasing number of observations).

Example: Party X estimated its CH₄ emissions from Manure management (livestock) using a default emission factor and animal population data for 1990 to 1998. In 1999 the Party began collecting data on animal feed intake and on manure storage systems at large farming operations. These data were used to revise the Party’s emission estimate for the year 2000, leading to an increase in emissions from 1999 to 2000. Similar data were not collected or available for the years prior to 2000. The Party’s estimates are not considered to be temporally consistent because different datasets (leading to different methods) were used over the time series. In order to make these estimates consistent, the Party should analytically recalculate its pre-2000 estimates (e.g., using IPCC Good Practice Guidance techniques) to eliminate as much as possible any time series biases.