Impact of misclassification on measures of cardiovascular disease mortality in the Islamic Republic of Iran: a cross-sectional study

OBJECTIVE: To assess the extent and pattern of misclassification of death from non-specific diagnoses emanating from the Iranian death registration system, and to correct the data for health policy and planning. METHODS: Detailed medical records for 1426 hospital deaths classified to seven ill-defined or vague causes of death were reviewed by trained physicians, who then completed standard death certificates. Underlying causes of death from the review were compared with the cause assigned in registration data. FINDINGS: The probable underlying pattern of causes of death in the Islamic Republic of Iran is substantially different to that suggested by the death registration system. About 88% of 582 cases with non-specific diagnoses at ages 15-69 years were reassigned to various specific causes including ischaemic heart disease (33%), stroke (13%) and injuries (10%). A similar pattern of misclassification is apparent for 738 deaths at older ages (70 years and over), with 46% being reassigned to ischaemic heart disease and stroke. CONCLUSION: A significant proportion of deaths in the Iranian death registration system are being classified to cause groups of little relevance to epidemiological research or health policy. Reassignment of these deaths would increase the proportion of deaths from ischaemic heart disease and cerebrovascular diseases each by 32%, diabetes mellitus by 68% and chronic lower respiratory diseases by 73%. Substantial changes to procedures for diagnosing causes of death are urgently required if registration data are to effectively guide health policies and programmes in the Islamic Republic of Iran.