title: Potential role of selection bias in the association between childhood leukemia and residential magnetic fields exposure: a population-based assessment.
abstract: OBJECTIVE
  Data from the Northern California Childhood Leukemia Study (NCCLS) were used to assess whether selection bias may explain the association between residential magnetic fields (assessed by wire codes) and childhood leukemia as previously observed in case-control studies.
  
  
  METHODS
  Wiring codes were calculated for participating cases, n=310; and non-participating cases, n=66; as well as for three control groups: first-choice participating, n=174; first-choice non-participating, n=252; and replacement (non-first choice participating controls), n=220.
  
  
  RESULTS
  Participating controls tended to be of higher socioeconomic status than non-participating controls, and lower socioeconomic status was related to higher wire-codes. The odds ratio (OR) for developing childhood leukemia associated with high wire-codes was 1.18 (95% CI: 0.85, 1.64) when all cases were compared to all first-choice controls (participating and non-participating). The OR for developing childhood leukemia in the high current category was 1.43 (95% CI: 0.91, 2.26) when participating cases were compared to first-choice participating controls, but no associations were observed when participating cases were compared to non-participating controls (OR=1.06, 95% CI: 0.71, 1.57) or to replacement controls (OR=1.06, 95% CI: 0.71, 1.60).
  
  
  CONCLUSIONS
  The observed risk estimates vary by type of control group, and no statistically significant association between wire codes and childhood leukemia is observed in the California population participating in the NCCLS.
authors.affiliation: School of Public Health, University of California, Berkeley, CA, United States. Electronic address: dannaaharon@gmail.com.
authors.forename: Danna A
authors.initials: DA
authors.lastname: Slusky
authors.affiliation: School of Public Health, University of California, Berkeley, CA, United States.
authors.forename: Monique
authors.initials: M
authors.lastname: Does
authors.affiliation: School of Public Health, University of California, Berkeley, CA, United States.
authors.forename: Catherine
authors.initials: C
authors.lastname: Metayer
authors.affiliation: Electric Power Research Institute, Palo Alto, CA, United States.
authors.forename: Gabor
authors.initials: G
authors.lastname: Mezei
authors.affiliation: School of Public Health, University of California, Berkeley, CA, United States.
authors.forename: Steve
authors.initials: S
authors.lastname: Selvin
authors.affiliation: School of Public Health, University of California, Berkeley, CA, United States.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Buffler
mesh_terms: D000293:Adolescent; D000328:Adult; D002140:California / Q000453:epidemiology; D016022:Case-Control Studies; D002648:Child; D005260:Female; D006801:Humans; D007938:Leukemia / Q000453:epidemiology* / Q000209:etiology; D060526:Magnetic Fields; D008297:Male; D012307:Risk Factors; D015983:Selection Bias; D012959:Socioeconomic Factors
keywords: Leukemia; Magnetic fields; Selection bias