title: Recovering physical activity missing data measured by accelerometers: a comparison of individual and group-centered recovery methods.
abstract: OBJECTIVE
  The purpose of this study was to determine which method, individual information-centered (IIC) or group information-centered (GIC), is more efficient in recovering missing physical activity (PA) data.
  
  
  METHODS
  A total of 2,758 Chinese children and youth aged 9 to 17 years old (1,438 boys and 1,320 girls) wore ActiGraph GT3X/GT3X+ accelerometers for 7 consecutive days. Those with no missing data (n = 900) were used to form a nonmissing sample, which, based on a semisimulation approach, was used to create a missing data set to evaluate a set of recovery methods, including 2 IIC and 22 GIC methods. Root mean square difference (RMSD), mean signed difference, and paired t test were used to determine the effectiveness of the recovery methods.
  
  
  RESULTS
  The smallest RMSD values, which represent the most accurate recovery, were found with: (a) GIC-Expectation-maximization (GIC-EM) regardless of gender and by age (113,957.64); (b) GIC-EM regardless of gender and age (114,367.88); (c) GIC-EM regardless of age and by gender (114,697.06); (d) GIC-EM by gender and age (116,178.34); and (e) IIC averaging of remaining days (125,851.23).
  
  
  CONCLUSIONS
  To recover 7-day PA accelerometer-determined activity missing data, we recommend using the GIC-EM and IIC approaches.
authors: Shanghai University of Sport, 399 Chang Hai Road, Shanghai 200438, PR China.
authors: Jie
authors: J
authors: Zhuang
authors: Shanghai University of Sport, 399 Chang Hai Road, Shanghai 200438, PR China.
authors: Peijie
authors: P
authors: Chen
authors: Shanghai University of Sport, 399 Chang Hai Road, Shanghai 200438, PR China.
authors: Chao
authors: C
authors: Wang
authors: Shanghai University of Sport, 399 Chang Hai Road, Shanghai 200438, PR China.
authors: Jing
authors: J
authors: Jin
authors: Shanghai University of Sport, 399 Chang Hai Road, Shanghai 200438, PR China.
authors: Zheng
authors: Z
authors: Zhu
authors: Shanghai University of Sport, 399 Chang Hai Road, Shanghai 200438, PR China.
authors: Wenjie
authors: W
authors: Zhang
mesh_terms: D061725:Accelerometry / Q000295:instrumentation*; D000293:Adolescent; D002648:Child; D002681:China; D003625:Data Collection; D003627:Data Interpretation, Statistical; D005260:Female; D015438:Health Behavior; D006306:Health Surveys; D006801:Humans; D008297:Male; D009043:Motor Activity