Biritwum, R. B., Minicuci, N., Maximova, T., Kalula, S., Arokiasamy, P., Salinas-Rodríguez, A., Manrique-Espinoza, B., Snodgrass, J. J., Sterner, K. N., Eick, G., Liebert, M. A., Schrock, J., Yawson, A. E., Kowal, P., Byles, J. E., Theou, O., Mensah, G. P., Naidoo, N., Wu, F., Guo, Y., Zheng, Y., Jiang, Y.. Elsevier; 2016. Prevalence of and factors associated with frailty and disability in older adults from China, Ghana, India, Mexico, Russia and South Africa.