Center Training, 5T32HD-07066-04, Mental Retardation and Other Developmental Disabilities, Earl Butterfield, May 29, 1980, Box: 12, Folder: 3. 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/452513 Accessed May 19, 2025.