Wilson MR, Van Houtven CH, Stearns S, Clipp EC. Depression and missed work among informal caregivers of older individuals with dementia. J Fam Econ Issues. 2007;28(4):684-98.
Cassingham KM, Sills EO, Pattanayak SK, Mansfield CA. Voluntary conservation of North Carolina's natural heritage. J For. 2002;100(5):16-23.