Indicator 15.5.1

Indicator Name, Target and Goal

Indicator 15.5.1: Red List Index

Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity and, by 2020, protect and prevent the extinction of threatened species

Goal 15: Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss

Definition and Rationale


The Red List Index is an index that measures changes in aggregate extinction risk across groups of species. It is based on the number of species in each category of extinction risk on The IUCN Red List of Threatened Species (IUCN 2015) is expressed as changes in an index ranging from 0 to 1. 

This is an indicator that is monitored at the global level.


Threatened species are those listed on The IUCN Red List of Threatened Species in the categories Vulnerable, Endangered, or Critically Endangered (i.e., species that are facing a high, very high, or extremely high risk of extinction in the wild in the medium-term future).

Rationale and Interpretation:

The world’s species are impacted by a number of threatening processes, including habitat destruction and degradation, overexploitation, invasive alien species, human disturbance, pollution and climate change. This indicator can be used to assess overall changes in the extinction risk of groups of species as a result of these threats and the extent to which threats are being mitigated. 

The Red List Index value ranges from 1 (all species are categorized as ‘Least Concern’) to 0 (all species are categorized as ‘Extinct’), and so indicates how far the set of species has moved overall towards extinction. A downward trend in the Red List Index over time means that the expected rate of future species extinctions is worsening (i.e., the rate of biodiversity loss is increasing). An upward trend means that the expected rate of species extinctions is abating (i.e., the rate of biodiversity loss is decreasing), and a horizontal line means that the expected rate of species extinctions is remaining the same, although in each of these cases it does not mean that biodiversity loss has stopped. 

The name “Red List Index” should not be taken to imply that the indicator is produced as a composite indicator of a number of disparate metrics (in the same way that, e.g., the Multidimensional Poverty Index is compiled). The index is compiled from data on changes over time in the Red List Category for each species, excluding any changes driven by improved knowledge or revised taxonomy. 

The Red List Index calculates the extinction risk of a group relative to the worst-case scenario where all species of that group would be Extinct.

Unit of measure:


Data Sources and Collection Method

Data sources:

Assessment of Red List index:

Data collection methods:

National agencies producing relevant data include government, non-governmental organisations (NGOs), and academic institutions working jointly and separately. Data are gathered from published and unpublished sources, species experts, scientists, and conservationists through correspondence, workshops, and electronic fora. 

Data are submitted by national agencies to IUCN, or are gathered through initiatives of the Red List Partnership. From 2013–6, the Red List Partnership encompassed: BirdLife International; Botanic Gardens Conservation International; Conservation International; Microsoft; NatureServe; Royal Botanic Gardens, Kew; Sapienza University of Rome; Texas A&M University; Wildscreen; and Zoological Society of London.

Data collection calendar: 2015

Data release calendar: Annual

Data providers: IUCN, Bangladesh Forest Department, Ministry of Environment, Forest and Climate Change

Data compilers: : IUCN, Bangladesh Forest Department, Ministry of Environment, Forest and Climate Change

Institutional mandate:

Method of Computation and Other Methodological Considerations

Computation Method:

The Red List Index is calculated for a specific time period by first multiplying the number of species in each Red List Category by a weight (ranging from 1 for ‘Near Threatened’ to 5 for ‘Extinct’ and ‘Extinct in the Wild’) and summing these values. This is then divided by a maximum threat score which is the total number of species multiplied by the weight assigned to the ‘Extinct’ category. This final value is subtracted from 1 to give the Red List Index value. 

Mathematically this calculation is expressed as: 

where Wc(t,s) is the weight for category c at time t for species s.

The weights are: for ‘Critically Endangered’ = 4, ‘Endangered’ = 3, ‘Vulnerable’ = 2, ‘Near Threatened’ = 1, ‘Least Concern’ = 0. ‘Critically Endangered’ species tagged as ‘Possibly Extinct’ or ‘Possibly Extinct in the Wild’ are assigned a weight of 5; WEX = 5, the weight assigned to ‘Extinct’ or ‘Extinct in the Wild’ species; and N is the total number of assessed species, excluding those assessed as Data Deficient in the current time period, and those considered to be ‘Extinct’ in the year the set of species was first assessed. 

In many cases, species lists will change slightly from one assessment to the next (e.g., owing to taxonomic revisions). The conditions can therefore be met by retrospectively adjusting earlier Red List categorizations using current information and taxonomy. This is achieved by assuming that the current Red List Categories for the taxa have applied since the set of species was first assessed for the Red List, unless there is information to the contrary that genuine status changes have occurred. Such information is often contextual (e.g., relating to the known history of habitat loss within the range of the species). If there is insufficient information available for a newly added species, it is not incorporated into the Red List Index until it is assessed for a second time, at which point earlier assessments are retrospectively corrected by extrapolating recent trends in population, range, habitat and threats, supported by additional information. 

Comments and limitations: 

There are four main sources of uncertainty associated with Red List Index values and trends:

(1) Inadequate, incomplete or inaccurate knowledge of a species’ status. This uncertainty is minimized by assigning estimates of extinction risk to categories that are broad in magnitude and timing;

(2) Delays in knowledge about a species becoming available for assessment. Such delays apply to a small (and diminishing) proportion of status changes, and can be overcome in the Red List Index through back-casting;

(3)Inconsistency between species assessments. These can be minimized by the requirement to provide supporting documentation detailing the best available data, with justifications, sources, and estimates of uncertainty and data quality, which are checked and standardized by IUCN through Red List Authorities, a Red List Technical Working Group and an independent Standards and Petitions Sub-committee; and

(4) Species that are too poorly known for the Red List Criteria to be applied are assigned to the Data In addition, the Red List Index does not capture particularly well the deteriorating status of common species that remain abundant and widespread but are declining slowly. 

Method of computation: 


Quality Management:

Quality Assurance:

Quality Assessment:

Data Disaggregation

The Red List Index can be downscaled to show national and regional Red List Indices, weighted by the fraction of each species’ distribution occurring within the country or region. These show an index of aggregate survival probability (the inverse of extinction risk) for all birds, mammals, amphibians, corals and cycads occurring within the country or region. The index shows how well species are conserved in a country or region to its potential contribution to global species conservation. 

This subset index is calculated as:

where t is the year of comprehensive reassessment, u is the spatial unit (i.e. country), W(t,s) is the weight of the global Red List category for species s at time t (Least Concern =0, Near Threatened =1, Vulnerable =2, Endangered =3, Critically Endangered =4, Critically Endangered (Possibly Extinct) =5, Critically Endangered (Possibly Extinct in the Wild) =5, Extinct in the Wild =5 and Extinct =5), WEX = 5 is the weight for Extinct species, Rsu is the fraction of the total range of species s in unit u, and Rs is the total range size of species s. 

The indicator can also be disaggregated by ecosystems, habitats, and other political and geographic divisions ,by taxonomic subsets, by suites of species relevant to particular international treaties or legislation,by suites of species exposed to particular threatening processes, and by suites of species that deliver particular ecosystem services, or have particular biological or life-history traits. In each case, information can be obtained from The IUCN Red List of Threatened Species to determine which species are relevant to particular subsets (e.g. which occur in particular ecosystems, habitats, and geographic areas of interest).

Comparability/ deviations from international standards


Official SDG Metadata URL

Internationally agreed methodology and guideline URL

Other references

International Union for Conservation of Nature. Internet Site.

International Organization(s) for Global Monitoring

This document was prepared based on inputs from International Union for Conservation of Nature (IUCN).

For focal point information for this indicator, please visit