The RLI method


A national scale Red List Index can be achieved in two ways:

  • Using existing data on global extinction risk – The global IUCN RLIs can be disaggregated to show trends at the national level.
  • Using National Red List data. If all species within a representative group have been assessed within a National Red List at least twice, an RLI can be calculated using these data.

RLIs can be calculated for any set of species that has been fully or representatively assessed at least twice using the same criteria.

RLIs are calculated using the number of species in each Red List category, and the number of species changing categories between assessments as a result of improvement or deterioration in threat status (Butchart et al. 2005). Essentially, it uses weight scores based on the Red List status of each of the sample species. Summing these scores across all species and relating them to the worst-case scenario – where all species are extinct – gives us an indication of how biodiversity is doing. Repeating the assessments over time will then allow us to see whether the extinction risk of biodiversity is overall increasing, decreasing or staying the same.