Fries B.E, Mehr D.R, Schneider D., Foley W.J, Burke R..  1993.  Mental dysfunction and resource use in nursing homes. Medical Care. 31(10):898-920.

Fries B.E, Ljunggren G., Winblad B..  1991.  International comparison of long-term care: the need for resident-level classification. Journal of the American Geriatrics Society. 39(1):10-6.