of the Deaf Population (NCDP) by Schein and Delk (1974). Based on a 1972 survey of the NCDP, Schein and Delk provided estimates consistent with a signing population between 250,000 and 500,000. The survey did not distinguish between ASL and other forms of signing; in fact, the name "ASL" was not yet in widespread use. Incorrect figures are sometimes cited for the population of ASL users in the United States based on misunderstandings of known statistics. Demographics of the deaf population have been confused with those of ASL use since adults who become deaf late in life rarely use ASL in the home. That accounts for currently-cited estimations that are greater than 500,000; such mistaken estimations can reach as high as 15,000,000. A 100,000-person lower bound has been cited for ASL users; the source of that figure is unclear, but it may be an estimate of prelingual deafness, which is correlated with but not equivalent to signing. ASL is sometimes incorrectly cited as the third- or fourth-most-spoken language in the United States. Those figures misquote Schein and Delk (1974), who actually concluded that ASL speakers constituted the third-largest population "requiring an interpreter in court". Although that would make ASL the third-most used language among monolinguals other than English, it does not imply that it is the fourth-most-spoken language in the United States since speakers of other languages may also speak English. Geographic distribution ASL is used throughout Anglo-America. That contrasts with Europe, where a variety of sign languages are used within the same continent. The unique situation of ASL seems to have been caused by the proliferation of ASL through schools influenced by the American School for the Deaf, wherein ASL originated, and the rise of community organizations for the Deaf. Throughout West Africa, ASL-based sign languages are signed by educated Deaf adults. Such languages, imported by boarding schools, are often considered by associations to be the official sign languages of their countries and are named accordingly, such as Nigerian Sign Language, Ghanaian Sign Language. Such signing systems are found in Benin, Burkina Faso, Ivory Coast, Ghana, Liberia, Mauritania, Mali, Nigeria, and Togo. Due to lack of data, it is still an open question how similar those sign languages are to the variety of ASL used in America. In addition to the aforementioned West African countries, ASL is reported to be used as a first language in Barbados, Bolivia, Cambodia