In our best cases the UNESCO and EGIDS language vitality and sustainability ratings that are assigned to a language are based on solid evidence gleaned from recent fieldwork. In other cases the rating has a less secure footing, for example because we have some but incomplete information, because we have good information but which is dated (in some cases more than two decades old), or because only a small part of a language community has been sampled. In order to separate those scores in which we are highly confident from those in which we have less confidence, UNESCO and EGIDS ratings are also assigned one of the reliability ratings shown in the following table.
|3||Fieldwork||Evidence is from recent fieldwork and direct observation in a representative sampling of locations.|
|2||Other Reliable Source||Evidence comes from non-linguistic sources, such as newspaper articles, online discussion forums or word of mouth, and seems reliable.|
|1||Best Guess||Even though evidence is meagre or anecdotal, perhaps even flawed, or is significantly dated, nevertheless we are willing to make a best guess or at least ‘pass on’ a value reported by others.|
|0||No Data||We have no information about language vitality, consequently no rating is assigned.|