Data deficient

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 usually indicates that little or no information is available on the abundance and distribution of the species. It can also indicate uncertainty about the taxonomic classification of an organism; for example, the IUCN classifies the orca as "data deficient" because of the likelihood that two or more types of the whale are separate 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).