"Report of an enquiry carried out from June 1961 of the beginning of 1962 in Nairobi, under the auspices of the Kenyan Ministry of Public Health — Survey of the factors which affect the difficulty of understanding graphs in order to increase the number of symbols used." (Jean-Marie Van Bol, Abdelfattah Fakhfakh: The use of mass media in the developing countries. Brussels: CIDESA, 1971 Nr. 1042, topic code 59)