Sampling Studies
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.
Fries, B. E., Nerenz, D. R., Falcon, S. P., Ashcraft, M. L., Lee, C. Z. 1990. A classification system for long-staying psychiatric patients. Medical Care. 28 (4) 311-23.