Observational studies:

Enloe M, et al.  Falls in Acute Care: An Academic Medical Center Six-Year Review.  J Patient Safety.  2005; 1(4): 208-214.
Retrospective study of falls at an academic medical center over 6 years.  RESULTS:  Table 2 shows the unadjusted annual fall rates were 5.86/1,000 patient days on the psychiatry units and Table 3 shows that broken down by age (regardless of service the patient was on), the fall rate for patients age 55-74 was 2.90/1,000 patient days and the rate for patients ages 75 and older was 4.08/1,000 patient days.

Schwendimann R, et al.  Characteristics of hospital inpatient falls across clinical departments.  Gerontology. 2008;54(6):342-8
Prospective study at 1,300 bed academic hospital over 13 weeks.  RESULTS:  Rate of falls on geriatrics units was 10.7/1,000 patient days.

Kerzman H, et al.  Characteristics of falls in hospitalized patients.  J Adv Nursing 2004; 47(2), 223–229.
Retrospective study of falls at a 2000-bed medical center in 1998.  RESULTS:  The rates of falls was 115/1,000 hospital admissions in the geriatric wards and 91 per 1,000 admissions in the psychiatric wards.  Rates per 1,000 inpatient days were not reported.