Counting the number of ASL speakers is difficult because ASL users have never been counted by the American census. ASL use in the general American population has not been directly measured. The ultimate source for current estimates of the number of ASL users in the United States is a report for the National Census 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.