Background: Research has associated some chronic conditions with self-harm and suicide. Quantifying such a relationship in mortality data relies on accurate death records and adequate techniques for identifying these conditions.
Objective: This study aimed to quantify the impact of identification methods for co-morbid conditions on suicides in individuals aged 30 years and older in Australia and examined differences by gender.
Method: A retrospective examination of mortality records in the National Coronial Information System (NCIS) was conducted. Two different methods for identifying co-morbidities were compared: International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10) coded data, which are provided to the NCIS by the Australian Bureau of Statistics, and free-text searches of Medical Cause of Death fields. Descriptive statistics and χ2 tests were used to compare the methods for identifying co-morbidities and look at differences by gender.
Results: Results showed inconsistencies between ICD-10 coded and coronial reports in the identification of suicide and chronic conditions, particularly by type (physical or mental). There were also significant differences in the proportion of co-morbid conditions by gender.
Conclusion: While ICD-10 coded mortality data more comprehensively identified co-morbidities, discrepancies in the identification of suicide and co-morbid conditions in both systems require further investigation to determine their nature (linkage errors, human subjectivity) and address them. Furthermore, due to the prescriptive coding procedures, the extent to which medico-legal databases may be used to explore potential and previously unrecognised associations between chronic conditions and self-harm deaths remains limited.
Keywords: cause of death; chronic disease; clinical coding; co-morbidity; death certificates; health information management; health information systems; suicide.