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 3 Physical activity and sedentary behavior 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: Sedentarya(min/d) Light-intensityb(min/day) MVPAc(min/day)
  Vertical axis Vector magnitude Vertical axis Vector magnitude Vertical axis Vector magnitude
Detailed-log 598.7 (537.3, 656.9) 518.5. (453.4, 585.3) 277.2 (227.6, 330.7) 343.8 (283.9, 404.0) 8.9 (2.7, 21.1) 19.7 (8.0, 37.7)
Limited-log + Troiano [5] 530.1 (480.1, 578.6) 474.6 (417.0, 529.6) 290.4 (242.2, 342.7) 358.7 (300.2, 418.4) 9.6 (3.0, 22.3) 20.7 (8.7, 38.7)
Limited log + Choi [11, 19] 581.6 (521.1, 639.8) 506.0 (439.2, 570.9) 287.9 (238.7, 340.7) 357.4 (297.4, 417.6) 9.4 (3.0, 22.1) 20.6 (8.7, 38.6)
  1. Note: All differences between vertical axis and vector magnitude (VM) were statistically significant P < 0.001. Includes all participants with at least 1 valid day (≥10 h wear-time) for particular assessment method.
  2. aSedentary time is defined as time during which the accelerometer registers vertical cpm <100 [21] and VM cpm <200 [18].
  3. bLight-intensity physical activity time is defined as time during which the accelerometer registers vertical cpm between 100 and 1951 [12] and VM cpm between 150 and 2690 [22].
  4. cMVPA time is defined as time during which the accelerometer registers vertical cpm > = 1952 [12] and VM cpm > = 2691 [22].
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BMC Public Health

ISSN: 1471-2458

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