title: Valid and invalid accelerometry data among children and adolescents: comparison across demographic, behavioral, and biological variables.
abstract: OBJECTIVE
  To examine whether there are differences between demographic, behavioral, and biological variables for those with invalid accelerometry data (IAD) and those with valid accelerometry data (VAD).
  
  
  METHODS
  Cross-sectional.
  
  
  METHODS
  Data from 2003-2006 National Health and Nutrition Examination Survey (NHANES) were used.
  
  
  METHODS
  Participants included 1,315 children (i.e., 6-11 years) with VAD and 534 children with IAD and 1,859 adolescents (i.e., 12-17 years) with VAD and 1,057 with IAD.
  
  
  METHODS
  Physical activity (PA) was measured using an accelerometer, with questionnaires used to assess demographic and behavioral variables and biological parameters assessed from a blood sample.
  
  
  METHODS
  Wald and design-based likelihood ratio tests and logistic regression were used to assess differences between those subjects with IAD and those with VAD.
  
  
  RESULTS
  After adjustments, overweight children, compared to normal weight children, were 1.6 (odds ratio [OR] = 1.67; 95% confidence interval [CI]: 1.22-2.29) times more likely to have IAD. After adjustments, and as an example, adolescents engaging in 4 or more hours of computer use per day, compared to no computer use, were 2.6 (OR = 2.6; 95% CI: 1.38-5.18) times more likely to have IAD.
  
  
  CONCLUSIONS
  Excluding youth with IAD may introduce bias, limit generalizability, and ultimately underestimate the association between PA and health outcomes. Future research is needed to identify reasons for poor monitoring compliance.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Loprinzi
authors.forename: Ellen
authors.initials: E
authors.lastname: Smit
authors.forename: Bradley J
authors.initials: BJ
authors.lastname: Cardinal
authors.forename: Carlos
authors.initials: C
authors.lastname: Crespo
authors.forename: Gary
authors.initials: G
authors.lastname: Brodowicz
authors.forename: Ross
authors.initials: R
authors.lastname: Andersen
mesh_terms: D061725:Accelerometry / Q000592:standards / Q000706:statistics & numerical data; D000293:Adolescent; D000294:Adolescent Behavior / Q000523:psychology; D015992:Body Mass Index; D002648:Child; D002652:Child Behavior / Q000523:psychology; D008076:Cholesterol, HDL / Q000097:blood; D003367:Cotinine / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology; D009749:Nutrition Surveys; D015203:Reproducibility of Results; D055105:Waist Circumference / Q000502:physiology
chemical_list: D008076:Cholesterol, HDL; D003367:Cotinine