title: Population-based versus hospital-based controls: are they comparable?
abstract: OBJECTIVE
  To compare whether there are differences among hospital and population controls.
  
  
  METHODS
  Two case-control studies were conducted on lung cancer risk factors in the Santiago de Compostela Public Health District. Whereas one used randomly chosen census-based population controls, the other used consecutive hospital controls that went to the reference hospital for non-smoking-related trivial interventions. The differences were analyzed using logistic regression. The dependent variable was type of control (hospital or population).
  
  
  RESULTS
  Hospital controls had a similar tobacco habit than population controls, but consumed more alcohol. For those consuming more than 50 ml daily, the risk of being a hospital control was 4.83 (95%CI: 2.55-9.14).
  
  
  CONCLUSIONS
  There may be some differences between hospital and population-based controls, which must be taken into account in the design of case-control studies. It is necessary to ascertain whether such differences are reproduced at other geographic locations and whether they can affect estimation of exposure-disease.
authors.affiliation: Department of Preventive Medicine and Public Health, University of Santiago de Compostela, Spain. alberto.ruano@usc.es
authors.forename: Alberto
authors.initials: A
authors.lastname: Ruano-Ravina
authors.forename: Mónica
authors.initials: M
authors.lastname: Pérez-Ríos
authors.forename: Juan Miguel
authors.initials: JM
authors.lastname: Barros-Dios
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D006801:Humans; D007297:Inpatients; D008175:Lung Neoplasms / Q000453:epidemiology*; D008875:Middle Aged; D011153:Population; D012307:Risk Factors