Amphibians - Threatened Species as Percent of Species Evaluated

Threatened species are those listed as Critically Endangered (CR), Endangered (EN) or Vulnerable (VU).

CRITICALLY ENDANGERED (CR)
A taxon is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered (see Section V), and it is therefore considered to be facing an extremely high risk of extinction in the wild.

ENDANGERED (EN)
A taxon is Endangered when the best available evidence indicates that it meets any of the criteria A to E for Endangered (see Section V), and it is therefore considered to be facing a very high risk of extinction in the wild.

VULNERABLE (VU)
A taxon is Vulnerable when the best available evidence indicates that it meets any of the criteria A to E for Vulnerable (see Section V), and it is therefore considered to be facing a high risk of extinction in the wild.
A part from the mammals, birds, amphibians and gymnosperms (i.e., those groups completely or almost completely evaluated), the figures in the last column are gross over-estimates of the percentage threatened due to biases in the assessment process towards assessing species that are thought to be threatened, species for which data are readily available, and under-reporting of Least Concern species. The true value for the percentage threatened lies somewhere in the range indicated by the two right-hand columns. In most cases this represents a very broad range. For example, the true percentage of threatened insects lies somewhere between 0.07% and 50%. Hence, although 39% of all species on the IUCN Red List are listed as threatened, this figure needs to be treated with extreme caution given the biases described above.

受威胁物种（Threatened species）指被列为极危（Critically Endangered, CR）、濒危（Endangered, EN）或易危（Vulnerable, VU）的类群。

极危（CR）
当现有最佳证据表明某一分类群（taxon）符合极危的标准A至E任意一项（详见第五章），则该分类群被视为在野外面临极高的灭绝风险。

濒危（EN）
当现有最佳证据表明某一分类群符合濒危的标准A至E任意一项（详见第五章），则该分类群被视为在野外面临很高的灭绝风险。

易危（VU）
当现有最佳证据表明某一分类群符合易危的标准A至E任意一项（详见第五章），则该分类群被视为在野外面临较高的灭绝风险。

除哺乳类、鸟类、两栖类及裸子植物（gymnosperms）（即已完成全部或近乎全部评估的类群）外，最后一列的受威胁物种占比数值存在严重高估。这一偏差源于评估过程存在偏倚：仅优先评估被认为受威胁、数据易于获取的物种，且对无危（Least Concern）物种的记录存在漏报。真实的受威胁百分比应介于右侧两列所示的区间内，多数情况下该区间跨度极大。例如，真实的受威胁昆虫占比介于0.07%至50%之间。因此，尽管世界自然保护联盟红色名录（IUCN Red List）中已有39%的物种被列为受威胁物种，但鉴于上述评估偏倚，对该数据需持极端谨慎的态度。