"Communication is defined broadly to include relevant material from such areas as agriculture, anthropology, community development, economics, education, law, political science, population, public administration, sociology, social psychology, and urban studies. Types of material covered are books, pamphlets, conference reports, seminar papers, theses and dissertations, research studies, surveys, government annual reports, commission reports, and periodical materials. Some of these are unpublished." (Eleanor Blum, Frances G. Wilhoit: Mass media bibliography. 3rd ed. Urbana: University of Illinois Press, 1990 Nr. 1635)