Tier Classification for Global SDG Indicators - UN
The UN has introduced a Tier Classification for Global SDG Indicators. To facilitate the implementation of the global indicator framework, all indicators are classified by the IAEG-SDGs into three tiers based on their level of methodological development and the availability of data at the global level. The first tier is when the indicator is conceptually clear and data are regularly produced by countries, the second when it is clear but data are not produced by countries and the third when there is no established methodology or standards yet.
All indicators are equally important, and the establishment of the tier system is intended solely to assist in the development of global implementation strategies.
Find out more about the concept here.