To estimate how much medieval literature once existed, book historians compare ancient book catalogs, which are incomplete, with the number and scope of surviving texts. Another estimate borrowed a technique from ecology called the “unseen species” model. The researchers turned to lists of surviving medieval texts—and those suspected to have been lost—written between 600 and 1450 C.E. in Dutch, French, Icelandic, Irish, English, and German. There were 3648 texts in total. When they ran those numbers through the unseen species model, the algorithm suggested just 9% of medieval texts from that period survived to the present day. That’s rather close to traditional estimates of 7%. The new study also broke things down by region: The model suggests only about 5% of English vernacular works have survived, compared with 17% and 19% for Icelandic and Irish vernacular works, respectively.

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