title: What is wrong with non-respondents? Alcohol-, drug- and smoking-related mortality and morbidity in a 12-year follow-up study of respondents and non-respondents in the Danish Health and Morbidity Survey.
abstract: OBJECTIVE
  Response rates in health surveys have diminished over the last two decades, making it difficult to obtain reliable information on health and health-related risk factors in different population groups. This study compared cause-specific mortality and morbidity among survey respondents and different types of non-respondents to estimate alcohol-, drug- and smoking-related mortality and morbidity among non-respondents.
  
  
  METHODS
  Prospective follow-up study of respondents and non-respondents in two cross-sectional health surveys.
  
  
  METHODS
  Denmark.
  
  
  METHODS
  A total sample of 39 540 Danish citizens aged 16 years or older.
  
  
  METHODS
  Register-based information on cause-specific mortality and morbidity at the individual level was obtained for respondents (n = 28 072) and different types of non-respondents (refusals n = 8954; illness/disabled n = 731, uncontactable n = 1593). Cox proportional hazards models were used to examine differences in alcohol-, drug- and smoking-related mortality and morbidity, respectively, in a 12-year follow-up period.
  
  
  RESULTS
  Overall, non-response was associated with a significantly increased hazard ratio (HR) of 1.56 [95% confidence interval (CI) = 1.36-1.78] for alcohol-related morbidity, 1.88 (95% CI = 1.38-2.57) for alcohol-related mortality, 1.55 (95% CI = 1.27-1.88) for drug-related morbidity, 3.04 (95% CI = 1.57-5.89) for drug-related mortality and 1.15 (95% CI = 1.03-1.29) for smoking-related morbidity. The hazard ratio for smoking-related mortality also tended to be higher among non-respondents compared with respondents, although no significant association was evident (HR = 1.14; 95% CI = 0.95-1.36). Uncontactable and ill/disabled non-respondents generally had a higher hazard ratio of alcohol-, drug- and smoking-related mortality and morbidity compared with refusal non-respondents.
  
  
  CONCLUSIONS
  Health survey non-respondents in Denmark have an increased hazard ratio of alcohol-, drug- and smoking-related mortality and morbidity compared with respondents, which may indicate more unfavourable health behaviours among non-respondents.
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: Anne Illemann
authors.initials: AI
authors.lastname: Christensen
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: Ola
authors.initials: O
authors.lastname: Ekholm
authors.affiliation: MRC/CSO Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK.|Department of Epidemiology, Columbia University, New York, NY.
authors.forename: Linsay
authors.initials: L
authors.lastname: Gray
authors.affiliation: Research Centre for Prevention and Health, The Capital Region of Denmark, Glostrup, Denmark.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Glümer
authors.affiliation: National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: Knud
authors.initials: K
authors.lastname: Juel
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000428:Alcohol Drinking / Q000453:epidemiology*; D019973:Alcohol-Related Disorders / Q000453:epidemiology; D003430:Cross-Sectional Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*; D019966:Substance-Related Disorders / Q000453:epidemiology*; D011795:Surveys and Questionnaires; D014029:Tobacco Use Disorder / Q000453:epidemiology; D055815:Young Adult
keywords: Alcohol; bias; cause-specific morbidity; cause-specific mortality; drug; health survey; non-response; smoking; survival
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