title: Youth recall and TriTrac accelerometer estimates of physical activity levels.
abstract: OBJECTIVE
  To examine significance of missing data and describe physical activity patterns using recall and accelerometer measures among youth in a nonlaboratory setting.
  
  
  METHODS
  Fifty-four middle-school students wore TriTrac-R3D monitors (TTM) and completed an interviewer-prompted 24-h recall during two, 5-d monitoring sessions. We coded 2860 30-min recall intervals to a standard MET compendium. Complete TTM data were gathered for 43 students. Ordinal multinomial models tested for bias in TTM estimates of activity levels due to: 1) exclusion of subjects with incomplete TTM data, and 2) exclusion of intervals within days due to missing TTM data.
  
  
  RESULTS
  Students with complete monitor data had an average 12.5 +/- 0.9 monitored hours per day over 5.5 +/- 2.1 d. Compared with students with incomplete monitoring data, they reported similar proportions of recall 30-min intervals at sedentary (68% vs 69%), light (14% vs 15%), moderate (11% vs 10%), and vigorous (7% vs 6%) intensity levels (P = 0.63). The proportion of recall intervals (within days) with and without simultaneous monitoring data did not differ by activity intensity (P = 0.64) across sedentary (69% vs 67%), light (14% vs 12%), moderate (11% vs 10%), and vigorous (6% vs 9%) categories. Recalls overestimated percent time per day in moderate and vigorous activity relative to TTM (22.8% vs 8.9%, P < 0.0001). Boys reported higher percent of time than girls in vigorous activity (10.9% vs 3.9%, P < 0.05). Girls reported more time than boys (9.5% vs 6.4%, P < 0.05) in light activities. No significant sex differences were observed using TTM.
  
  
  CONCLUSIONS
  Missing TTM data did not bias estimates of activity levels. Self-reported activity measures overestimated moderate and vigorous activity relative to the TTM and varied by sex.
authors.affiliation: Department of Society, Human Development and Health, Harvard School of Public Health, Boston, MA 02115, USA. acradock@hsph.harvard.edu
authors.forename: Angie L
authors.initials: AL
authors.lastname: Cradock
authors.forename: Jean L
authors.initials: JL
authors.lastname: Wiecha
authors.forename: Karen E
authors.initials: KE
authors.lastname: Peterson
authors.forename: Arthur M
authors.initials: AM
authors.lastname: Sobol
authors.forename: Graham A
authors.initials: GA
authors.lastname: Colditz
authors.forename: Steven L
authors.initials: SL
authors.lastname: Gortmaker
mesh_terms: D000293:Adolescent; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000379:methods / Q000706:statistics & numerical data; D008991:Monitoring, Physiologic / Q000379:methods* / Q000706:statistics & numerical data; D012737:Sex Factors; D013334:Students