Christensen T, Riis AH, Hatch EE, Wise LA, Nielsen MG, Rothman KJ, Toft Sorensen H, Mikkelsen EM. Costs and efficiency of online and offline recruitment methods: a web-based cohort study. J Med Internet Res. 2017 Mar 1;19(3):e58. doi: 10.2196/jmir.6716
McDonald R, Mead N, Cheraghi-Sohi S, Bower P, Whalley D. Governing the ethical consumer: identity, choice and the primary care medical encounter. Sociol Health Illn. 2007 Apr 1;29(3):430-56.
Cassingham KM, Sills EO, Pattanayak SK, Mansfield CA. Voluntary conservation of North Carolina's natural heritage. J For. 2002;100(5):16-23.