Whittington D, Sur D, Cook J, Chatterjee S, Maskery B, Lahiri M, Poulos C, Boral S, Nyamete A, Deen J, Ochiai L, Bhattacharya SK. Rethinking cholera and typhoid vaccination policies for the poor: private demand in Kolkata, India. World Dev. 2009 Feb 1;37(2):399-409.
Cassingham KM, Sills EO, Pattanayak SK, Mansfield CA. Voluntary conservation of North Carolina's natural heritage. J For. 2002;100(5):16-23.