title: Reliability of accelerometric measurement of physical activity in older adults-the benefit of using the trimmed sum.
abstract: There is general consensus that physical activity is important for preserving functional capacities of older adults and positively influencing quality of life. While accelerometry is widely accepted and applied to assess physical activity in studies, several problems with this method remain (e.g., low retest reliability, measurement errors). The aim of this study was to test the intra-instrumental retest reliability of a wrist-worn accelerometer in a 3-day measurement of physical activity in older adults and to compare different estimators. A sample of 123 older adults (76.5 ± 5.1 years, 59 % female) wore a uniaxial accelerometer continuously for 1 week. The data were split into two repeated measurement values (week set) of 3 days each. The sum, the 80-99th quantiles and the 80-99th trimmed sums were built for each week set. Retest reliability was assessed for each estimator and graphically demonstrated by Bland-Altman plots. The intraclass correlation of the retest reliability ranged from 0.22 to 0.91. Retest reliability increases when a more robust estimator than the overall sum is used. Therefore, the trimmed sum can be recommended as a conservative estimate of the physical activity level of older adults.
authors.affiliation: Department of Sports Medicine and Sports Nutrition, Ruhr-University Bochum, 44801 Bochum, Germany  ; Department of Medical Informatics, Biometry and Epidemiology, Ruhr-University Bochum, 44801 Bochum, Germany.
authors.forename: Ulrike Sonja
authors.initials: US
authors.lastname: Trampisch
authors.forename: Petra
authors.initials: P
authors.lastname: Platen
authors.forename: Matthias
authors.initials: M
authors.lastname: Trampisch
authors.forename: Anna
authors.initials: A
authors.lastname: Moschny
authors.forename: Ulrich
authors.initials: U
authors.lastname: Thiem
authors.forename: Timo
authors.initials: T
authors.lastname: Hinrichs