Methods used in the 1982, 1993, and 2004 birth cohort studies from Pelotas, Rio Grande do Sul State, Brazil, and a description of the socioeconomic conditions of participants’ families - Barros, AJD; Santos, IS; Matijasevich, A; Araújo, CL; Gigante, DP; Menezes, AMB; Horta, BL; Tomasi, E; Victora, CG; Barros, FC (Cad Saude Publica, 2008)