1. Burnside LM. Nursing and the aged: A self-care approach St. Louis: McGraw-Hill 1988.
2. Butler R. Lewis M. Aging and mental health: Positive psychosocial and biomedical approaches 3rd ed. St. Louis: CV Mosby 1982.
3. Campbell D.T. Stanley J.C. Experimental and quasi-experimental designs for research. Chicago: Rand McNaIIy 1963.
4. Colsher P.L. Data quality and age: Health and psychobehavioral correlates of item nonresponse and inconsistent responses. J Gerontol 1989; 44.P45-P52.
5. Cook T.D. Campbell D.T. Quasi-experimentation design and analysis issues for field settings. Chicago: Rand McNaIIy College Publishing Co 1979.