Center Training, 5T32HD-07066-04, Mental Retardation and Other Developmental Disabilities, Earl Butterfield, February, 27, 1980, Box: 12, Folder: 2. University of Kansas Schiefelbusch Institute for Life Span Studies records, RG 35. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/452512 Accessed May 16, 2025.