[1] Univ Fed Rio Grande do Sul, Fac Med, BR-90880480 Porto Alegre, RS, Brazil
[2] Hosp Femina, Grp Hosp Conceicao, Porto Alegre, RS, Brazil
[3] Univ Fed Rio Grande do Sul, Inst Matemat, Dept Estat, BR-90880480 Porto Alegre, RS, Brazil
[4] Univ Auckland, Auckland 1, New Zealand
[5] Univ Tesside, Middlesbrough, Guisborough, England
[6] S Cleveland Hosp, Middlesbrough, Guisborough, England
[7] Univ Extremadura Sul Catarinense, Sch Med, Criciuma, Brazil
[8] Fundacao Fac Fed Ciencias Med Porto Algre, Dept Epidemiol, Porto Alegre, RS, Brazil