Catalog of Not Fully Assessed Species

A data deficient (DD) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as offering insufficient information for a proper assessment of conservation status to be made. This does not necessarily indicate that the species has not been extensively studied; but it does indicate that little or no information is available on the abundance and distribution of the species.
The IUCN recommends that care be taken to avoid classing species as "data deficient" when the absence of records may indicate dangerously low abundance: "If the range of a taxon is suspected to be relatively circumscribed, if a considerable period of time has elapsed since the last record of the taxon, threatened status may well be justified" (see also precautionary principle).
A not evaluated (NE) species is one which has been categorized under the IUCN Red List of threatened species as not yet having been assessed by the International Union for Conservation of Nature.
This conservation category is one of nine IUCN threat assessment categories for species to indicate their risk of global extinction. The categories range from 'extinct' (EX) at one end of the spectrum, to 'least concern' (LC) at the other. The categories 'data deficient' and 'not evaluated' (NE) are not on the spectrum, because they indicate species that have not been reviewed enough to assign to a category.
The category of 'not evaluated' does not indicate that a species is not at risk of extinction, but simply that the species has not yet been studied for any risk to be quantified and published. The IUCN advises that species categorised as 'not evaluated' "...should not be treated as if they were non-threatened. It may be appropriate ... to give them the same degree of attention as threatened taxa, at least until their status can be assessed."
By 2015, the IUCN had assessed and allocated conservation statuses to over 76,000 species worldwide. From these it had categorised some 24,000 species as globally threatened at one conservation level or another. However, despite estimates varying widely as to the number of species existing on Earth (ranging from 3 million up to 30 million), this means the IUCN's 'not evaluated' (NE) category is by far the largest of all nine extinction risk categories.
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