Indoor and outdoor falls in older adults are different: the maintenance of balance, independent living, intellect, and Zest in the Elderly of Boston Study

Objectives: To identify risk factors for indoor and outdoor falls.

Design: Prospective cohort study.

Setting: The MOBILIZE Boston Study, a study of falls etiology in community-dwelling older individuals.

Participants: Seven hundred sixty-five women and men, mainly aged 70 and older, from randomly sampled households in the Boston, Massachusetts, area.

Measurements: Baseline data were collected by questionnaire and comprehensive clinic examination. During follow-up, participants recorded falls on daily calendars. The location and circumstances of each fall were asked during telephone interviews.

Results: Five hundred ninety-eight indoor and 524 outdoor falls were reported over a median follow-up of 21.7 months. Risk factors for indoor falls included older age, being female, and various indicators of poor health. Risk factors for outdoor falls included younger age, being male, and being relatively physically active and healthy. For instance, the age- and sex-adjusted rate ratio for having much difficulty or inability to perform activities of daily living relative to no difficulty was 2.57 (95% confidence interval (CI) = 1.69-3.90) for indoor falls but 0.27 (95% CI = 0.13-0.56) for outdoor falls. The rate ratio for gait speed of less than 0.68 m/s relative to a speed of greater than 1.33 m/s was 1.48 (95% CI = 0.81-2.68) for indoor falls but 0.27 (95% CI = 0.15-0.50) for outdoor falls.

Conclusion: Risk factors for indoor and outdoor falls differ. Combining these falls, as is done in many studies, masks important information. Prevention recommendations for noninstitutionalized older people would probably be more effective if targeted differently for frail, inactive older people at high risk for indoor falls and relatively active, healthy people at high risk for outdoor falls.