"The growth of educational publishing in Kenya depends heavily on the disposable income of its customers. This article looks at the incomes of both actual and potential customers, and how they prioritize their spending. The findings are based on extensive research carried out by the author between 1997 and 2000 (see also entry 624 above), revised and updated in 2003. In selecting the areas to conduct the research, socio-economic factors, geographical conditions and level of development were considered. It was found that most textbook purchasers think that textbooks are very expensive in comparison with their income levels. The study also demonstrated that the rate at which textbook prices increase is higher than the increase in income levels, and, as a result, there will always be a shortage of textbooks in schools, and in the homes of consumers as they will always choose their own priorities: "Textbooks will always be the last of the priorities of most Kenyans, as they will search for the essential commodities of life first. Although the government is planning to purchase textbooks for primary schools, the problem will still persist as the books bought for use in schools will be only the recommended textbooks, while parents will still be buying supplementary textbooks." (Hans M. Zell, Publishing, Books & Reading in Sub-Saharan Africa, 3d ed. 2008, nr. 625)