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Edit on GitHubIUCN Red List Categories and Criteria
Assessments are based on 5 objective, scientific criteria, each containing a set of quantitative thresholds against which the risk of extintion of a species can be assessed. Species must be assessed against all criteria during an assessment.
These 5 criteria are:
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Criterion A - Popluation reduction
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Criterion B - Restricted geographic range
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Criterion C - Small population size and decline
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Criterion D - Very small or restricted population
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Criterion E - Quantitative analysis
Each of these criteria has a set of associated thresholds for these biological traits that allow assessors to assess the risk of exinction for that species and apply one of 9 categories.
All criteria shoudl be applied to a taxon during an assessment and it is the criterion with the highest threat category that is used as the final Red List assessment.