abstract: Does smoking kill? A study of death certification and smoking -- Proctor et al. 65 (2): 129 -- Journal of Clinical Pathology

Conclusion
This study demonstrates that smoking is rarely cited on death certificates, even in cases where the causal link with smoking is very strong. There are many reasons why smoking is not cited on death certificates. One frequently cited reason is the reluctance of doctors to stigmatise the deceased. Interestingly, such reluctance did not extend to citing alcohol as a COD. By not recording smoking on death certificates doctors are failing to gather important epidemiological and pathological data.