Corrigendum: Medical residency in Portugal: a cross-sectional study on the working conditions - José Chen-Xu; José Chen-Xu; Bruno Miranda Castilho; Bruno Moura Fernandes; Diana Silva Gonçalves; André Ferreira; Ana Catarina Gonçalves; Maycoll Ferreira Vieira; Andreia M. Silva; Fábio Borges; Mónica Paes Mamede (Frontiers in Health Services)