Mor V., Branco K., Fleishman J., Hawes C., Phillips C., Morris J., Fries B..  1995.  The structure of social engagement among nursing home residents. Journals of Gerontology Series B-Psychological Sciences & Social Sciences. 50(1):P1-P8.

Buttar A., Blaum C., Fries B..  2001.  Clinical characteristics and six-month outcomes of nursing home residents with low activities of daily living dependency. J Gerontol A Biol Sci Med Sci. 56(5):M292-7.