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

AIM 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. DESIGN Prospective follow-up study of respondents and non-respondents in two cross-sectional health surveys. SETTING Denmark. PARTICIPANTS A total sample of 39 540 Danish citizens aged 16 years or older. MEASUREMENTS 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. FINDINGS 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. CONCLUSION 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.