Educational Status
        Yoo, In-Young 2011. Analysis of multi-variate recurrent fall risk factors in elderly people using residential assessment instrument-home care-comparisons between single and recurrent fallers. Journal of Korean Academy of Nursing.  41 (1) 119-128.  
          Perls, T. T., Morris, J. N., Ooi, W. L., Lipsitz, L. A. 1993. The relationship between age, gender and cognitive performance in the very old: the effect of selective survival. Journal of the American Geriatrics Society.  41 (11) 1193-201.  
          Hirdes, J. P., Forbes, W. F. 1992. The importance of social relationships, socioeconomic status and health practices with respect to mortality among healthy Ontario males. Journal of Clinical Epidemiology.  45 (2) 175-82.