Initiated in 2005, The MOBILIZE Boston Study is a prospective cohort study to identify risk factors and underlying mechanisms of falls for Massachusetts elders, including the roles of cerebral hypoperfusion, peripheral sensory deficits, musculoskeletal pain, and foot disorders (3
). Conducted by the Institute for Aging Research at Hebrew SeniorLife (Boston) and funded by the US National Institute on Aging, The MOBILIZE Boston Study has enrolled 765 individuals aged 70 years or older and is following them for the occurrence of falls over a 2-year period. Participants were randomly selected for recruitment by using town lists and were required to complete a 3-stage eligibility screening procedure including 1) an initial “doorstep visit” at the randomly selected household, 2) a telephone interview, and 3) an interviewer-administered questionnaire at the home of the respondent.
Participants underwent comprehensive assessments, including a home visit and a clinic examination. At the home visit, trained interviewers administered a standardized questionnaire that covers demographic characteristics, medical history (4
), medications (5
), falls history, self-efficacy regarding avoidance of falls (6
), fracture history, pain assessments (7
), vision and hearing, footwear (9
), physical activity (11
), cigarette smoking (12
), social supports (13
), bladder and bowel function, sleep and energy, depression (14
), syncope, restricted-activity days, activities of daily living (15
), and neuropsychological and mental status assessments (17
). During the home visit, study interviewers instructed participants on how to use a “falls calendar” to record whether or not a fall occurred each day (“F” to denote a fall and “N” for no fall) (19
). The 12-month falls calendars were affixed to a magnetized backing for placement in a highly visible location in the home, such as a refrigerator door. Each month of the falls calendar was located on a detachable prepaid postcard that respondents mailed to the study office upon completion.
During the clinic visit, a research nurse administered a standardized examination including measurements of height, weight, postural blood pressure, visual acuity, static balance (20
), and lower limb strength. In addition, the participant underwent venipuncture and transcranial Doppler measurements of cerebral blood flow (21
). The clinical examination included the Short Physical Performance Battery (22
), a foot disorder evaluation (23
), a musculoskeletal examination (25
), a manual tender point survey (28
), and somatosensory function tests (29
Although we used previously validated instruments for data collection whenever possible (3
), it was not feasible to test reliability of screening procedures such as the Mini-Mental State Examination. However, very few individuals (n
8) were excluded because of cognitive impairment. We did conduct reliability testing for carbon dioxide vasoreactivity. The intraclass correlation coefficient was 0.92 for 2 transcranial Doppler measurements performed 6 months apart in 21 elderly volunteers.
Follow-up examinations were originally planned for 12 and 24 months after baseline assessments. Because of an unanticipated high rate of ineligibility because of language barriers that necessitated unexpectedly large amounts of time and resources to recruit and conduct study procedures, we were advised by our scientific advisory board to change the number of follow-up examinations to 1 assessment at 18 months. This change significantly reduced not only study costs but also subject burden. On the other hand, study power was reduced for aims that included changes in function as outcomes.
For example, the power to detect a 0.01 standard deviation difference in change in gait speed between 2 groups of 250 individuals was reduced from 91% when using 2 measurements at 12 and 24 months of follow-up to 81% when using 1 follow-up measurement over 18 months (alpha
0.5 between measures). Thus, while the protocol change to only 1 follow-up visit resulted in a loss of power, the reduction was moderate, and power still remained adequate. Since 1 primary aim of our study was to identify novel risk factors for falls, which were assessed not at follow-up visits but by monthly calendars for the 5-year duration of the study, the change in follow-up frequency did not limit our ability to achieve our primary aims.