Validation and internal consistency of Patient Health Questionnaire-9 for major depression in Parkinson's disease - Chagas, Marcos Hortes Nisihara; Tumas, Virot; Rodrigues, Guilherme R.; Machado-de-Sousa, João Paulo; Santos Filho, Alaor; Hallak, Jaime Eduardo Cecílio; Crippa, José Alexandre de Souza (Age and Ageing, 2013)