The IAEG-SDG categorizes the indicators into three different tiers, based on the maturity of the methodology and the extent of the data collection, defined as follows:
- Tier I indicators have established methodologies and data regularly produced by a critical mass of countries
- Tier II indicators have established methodologies but data are not regularly produced by countries
- Tier III indicators have methodologies that are under development
All indicators are equally important, and the purpose of the categorization is to make sure that due attention is paid to developing methodologies and implementing data collection for tier II and III indicators, with a strong focus on country capacity-building.
The final indicator framework, as adopted by the United Nations Statistical Commission in March 2017, includes about 230 indicators. The IAEG-SDG will continue to refine the indicator framework throughout the SDG period, including revising the tier classification on a yearly basis. The first revision of the framework is scheduled for 2020.