Kovacs, Diane K.
The virtual reference handbook : interview and information delivery techniques for the chat and e-mail environments
Facet Publishing, 2007
 Buku Referensi
Hani Kusumaningsih
Evaluasi layanan referensi e-mail Perpustakaan United Nations Information Centre Jakarta = Evaluation of e-mail reference at United Nations Information Centre Library Jakarta
Fakultas Ilmu Pengetahuan Budaya Universitas Indonesia, 2016
 UI - Skripsi Membership
Liu, Jia
The Evaluation of worldwide digital reference services in libraries
Chandos Publishing, 2007
 Buku Teks SO
Evaluation of reference services
edited by Bill Katz and Ruth A. Fraley
Haworth Press, 1984
 Buku Referensi
Cassell, Kay Ann
Reference and information services : an introduction
Neal-Schuman, an imprint of the American Library Association, 2013
 Buku Teks SO