Souza, Luccas Melo de, et al. “Voluntary Work, Demographic, Social and Economic Features and Health Self-Perception by Elderly People from Porto Alegre (Brazil)”. Revista Da Escola De Enfermagem Da USP, vol. 44, no. 3, Sept. 2010, pp. 561-9, https://doi.org/10.1590/S0080-62342010000300003.