title: Modeling errors in physical activity recall data.
abstract: BACKGROUND
  Physical activity recall instruments provide an inexpensive method of collecting physical activity patterns on a sample of individuals, but they are subject to systematic and random measurement error. Statistical models can be used to estimate measurement error in activity recalls and provide more accurate estimates of usual activity parameters for a population.
  
  
  METHODS
  We develop a measurement error model for a short-term activity recall that describes the relationship between the recall and an individual's usual activity over a long period of time. The model includes terms for systematic and random measurement errors. To estimate model parameters, the design should include replicate observations of a concurrent activity recall and an objective monitor measurement on a subsample of respondents.
  
  
  RESULTS
  We illustrate the approach with preliminary data from the Iowa Physical Activity Measurement Study. In this dataset, recalls tend to overestimate actual activity, and measurement errors greatly increase the variance of recalls relative to the person-to-person variation in usual activity. Statistical adjustments are used to remove bias and extraneous variation in estimating the usual activity distribution.
  
  
  CONCLUSIONS
  Modeling measurement error in recall data can be used to provide more accurate estimates of long-term activity behavior.
authors.affiliation: Dept of Statistics, Iowa State University, Ames, IA, USA.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Nusser
authors.forename: Nicholas K
authors.initials: NK
authors.lastname: Beyler
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Welk
authors.forename: Alicia L
authors.initials: AL
authors.lastname: Carriquiry
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Fuller
authors.forename: M N
authors.initials: MN
authors.lastname: King B
mesh_terms: D001288:Attention; D004734:Energy Metabolism; D004812:Epidemiologic Methods; D006302:Health Services Research; D006801:Humans; D011939:Mental Recall; D008960:Models, Psychological; D015233:Models, Statistical; D009043:Motor Activity / Q000502:physiology*; D012107:Research Design; D057185:Sedentary Behavior; D015983:Selection Bias; D013223:Statistics as Topic; D013997:Time Factors