Prevalence and socio-demographic correlates of poor sleep quality among older adults in Hebei province, China. - Zhang, Yun-Shu; Jin, Yu; Rao, Wen-Wang; Jiang, Yuan-Yuan; Cui, Li-Jun; Li, Jian-Feng; Li, Lin; Ungvari, Gabor S.; Ng, Chee H.; Li, Ke-Qing; Xiang, Yu-Tao (Scientific Reports, 2020)