title: Cell phone use and crash risk:  evidence for positive bias.
abstract: BACKGROUND
  Recent epidemiologic studies have estimated little or no increased risk of automotive crashes related to cell phone conversations by the driver, whereas earlier case-crossover studies estimated the relative risk as close to 4. Did earlier studies introduce a positive bias in relative risk estimates by overestimating driving exposure in control windows?
  
  
  METHODS
  Driving exposures in a "control" window and a corresponding "case" window on the subsequent day were tabulated across 100 days for 439 GPS-instrumented vehicles in the Puget Sound area during 2005-2006.
  
  
  RESULTS
  For control windows containing at least some driving, driving exposure was about one-fourth that of case windows. Adjusting for this imbalance reduces relative risk estimates in the earlier case-crossover studies from 4 to 1.
  
  
  CONCLUSIONS
  Earlier case-crossover studies likely overestimated the relative risk for cell phone conversations while driving by implicitly assuming that driving during a control window was full-time when it may have been only part-time.
authors.affiliation: Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, MI 48201, USA. ryoun@med.wayne.edu
authors.forename: Richard A
authors.initials: RA
authors.lastname: Young
mesh_terms: D000063:Accidents, Traffic / Q000706:statistics & numerical data*; D015982:Bias; D040421:Cell Phone / Q000706:statistics & numerical data; D040362:Geographic Information Systems; D006801:Humans; D012306:Risk; D012307:Risk Factors; D014861:Washington / Q000453:epidemiology