Souza, L. M. de; Lautert, L.; Hilleshein, E. F. Voluntary Work, Demographic, Social and Economic Features and Health Self-Perception by Elderly People from Porto Alegre (Brazil). Rev. Esc. Enferm. USP 2010, 44 (3), 561-569. https://doi.org/10.1590/S0080-62342010000300003.