7-days of valid data). Using only dates from the log and the Choi algorithm yielded: 1) larger samples with valid data than using log dates and times, 2) similar wear-times as using log dates and times, 3) more wear-time (V, 48.1 min more; VM, 29.5 min more) than only log dates and Troiano algorithm. Wear-time algorithm impacted sedentary time (~30-60 min lower for Troiano vs. Choi) but not moderate-to-vigorous (MV) PA time. Using V-axis cut-points yielded ~60 min more sedentary time and ~10 min less MVPA time than using VM cut-points. Conclusions Combining log-dates and the Choi algorithm was optimal, minimizing missing data and researcher burden. Estimates of time in physical activity and sedentary behavior are not directly comparable between V-axis and VM cut-points. These findings will inform consensus development for accelerometer data processing in ongoing epidemiologic studies."/>
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Table 2 Accelerometer wear time estimates using data from vertical axis only and from vector magnitude assessment, Women's Health Study, 2011-2013

From: Impact of accelerometer data processing decisions on the sample size, wear time and physical activity level of a large cohort study

Assessment method: Women with ≥1 valid day Women with ≥4 valid days Number of valid days Wear-time on valid days (min)
  N (%) N (%) Median (IQR) Median (IQR)
  Vertical Vector magnitude Vertical Vector magnitude Vertical Vector magnitude Vertical Vector magnitude
Detailed-log 6834 (89.3) 6834 (89.3) 6741 (88.1) 6741 (88.1) 7 (7, 7) 7 (7, 7) 898.0 (850.7, 937.4) 898.0 (850.7, 937.4)
Troiano [5] 7435(97.2) 7458 (97.5) 7202 (94.1) 7312 (95.6) 7 (7, 8) 8 (7, 9) 838.3 (786.8, 886.7) 860.0 (812.5, 904.0)
Choi [11, 19] 7485 (97.8) 7494 (98.0) 7360 (96.2) 7378 (96.4) 9 (8, 9) 9 (8, 10) 875.7 (832.3, 917.0) 887.0 (845.2, 928.2)
Limited-log + Troiano 7383 (96.5) 7391 (96.6) 7110 (96.9) 7188 (94.0) 7, (6, 7) 7 (7, 7) 842.3 (788.7, 890.9) 866.8 (813.3, 912.3)
Limited-log + Choi 7396(96.7) 7396 (96.7) 7247(94.7) 7258 (94.9) 7 (7, 7) 7 (7, 7) 890.4 (841.6, 933.6) 896.4 (848.4, 939.5)
  1. Note: Detailed-log refers to data from participant logs that make use of date and time (hour, minute, Am/PM) that the monitor was put on and off.
  2. Limited-log refers to data from participant logs that make use of date only (no time information used).
  3. Limited-log + algorithm used date of wear from participant logs and time on/off from respective algorithm.
  4. Valid days are defined by convention as those with ≥10 hours wear-time.
  5. Percent values are the N divided by 7650 (eligible sample).