In the IPCC Guidelines and Good Practice Guidance, methods are generally referred to as “Tiers”, with higher tier methods being more advanced.

The IPCC Good Practice Guidance provides decision trees to help Parties in the selection of data and methods (i.e., Tiers) for each individual category. These decision trees are intended to direct the Party to use the best method and data possible, given its national circumstances.

In general, it is good practice for Parties to utilize higher tier methods, with their associated more detailed data, in particular for key categories.

Parties are, however, permitted some flexibility in applying these decision trees as long as the choices made by the Party result in estimates that are of equivalent quality to those described in the IPCC Good Practice Guidance.

This flexibility is an important characteristic of the IPCC Guidelines and the Good Practice Guidance because it recognizes that parties have different national circumstances (e.g., availability of historical data). Although good practice is meant to direct Parties to use more rigorous methods and more detailed data, what is defined as “good practice” can vary from Party to Party depending on its own unique features.