title: Combining individual- and group-level exposure information: child carbon monoxide in the Guatemala woodstove randomized control trial.
abstract: BACKGROUND
  Epidemiology frequently relies on surrogates of long-term exposures, often either individual-level short-term measurements or group-level based on long-term characteristics of subjects and their environment. Whereas individual-level measures are often imprecise due to within-subject variability, group-level measures tend to be inaccurate due to residual between-subject variability within groups. Rather than choose between these error-prone estimates, we borrow strength from each by use of mixed-model prediction and we compare the predictive validity.
  
  
  METHODS
  We compared alternative measures of long-term exposure to carbon monoxide (CO) among children in the RESPIRE woodstove randomized control trial during years 2003 and 2004. The main study included 1932 repeated 48-hour-average personal CO measures among 509 children from 0-18 months of age. We used a validation study with additional CO measures among a random subsample of 70 of the children to compare the predictive validity of individual-level estimates (based on observed short-term exposures), group-level estimates (based on stove type and other residential characteristics), and mixed-model predictions that combine these 2 sources of information.
  
  
  RESULTS
  The estimated error variance for mixed-model prediction was 63% lower than the individual-level measure based on the exposure data and 58% lower than the corresponding group-level measure.
  
  
  CONCLUSIONS
  When both individual- and group-level estimates are available but imperfect, mixed-model prediction may provide substantially better measures of long-term exposure, potentially increasing the sensitivity of epidemiologic studies to underlying causal relations.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA 02215, USA. jmccrack@hsph.harvard.edu
authors.forename: John P
authors.initials: JP
authors.lastname: McCracken
authors.forename: Joel
authors.initials: J
authors.lastname: Schwartz
authors.forename: Nigel
authors.initials: N
authors.lastname: Bruce
authors.forename: Murray
authors.initials: M
authors.lastname: Mittleman
authors.forename: Louise M
authors.initials: LM
authors.lastname: Ryan
authors.forename: Kirk R
authors.initials: KR
authors.lastname: Smith
mesh_terms: D000293:Adolescent; D000328:Adult; D016902:Air Pollution, Indoor / Q000032:analysis*; D002248:Carbon Monoxide / Q000032:analysis*; D003296:Cooking; D004812:Epidemiologic Methods; D005260:Female; D006166:Guatemala; D006801:Humans; D017745:Incineration / Q000379:methods*; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008962:Models, Theoretical; D054928:Validation Studies as Topic; D055815:Young Adult
chemical_list: D002248:Carbon Monoxide