9Altaf, M. A. and Hughes, J. A., 1994, “Measuring the Demand for Improved Urban Sanitation Services: Results of a Contingent Valuation Study in Ouagadougou, Burkina Faso”,Urban Studies, Vol.31, pp.l763-1776.
10Andreia C. Santos, Jennifer A. Roberts, Mauricio L. Barreto and Sandy Caimcross, 2011,“Demand for Sanitation in Salvador, Brazil: A Hybrid Choice Approach”,Social Science & Medicine, Vol.72, pp.l325-1332.