Validity and utilization of epidemiological data: a study of ischaemic heart disease and coronary risk factors in a local population.

Objectives: To calculate the burden of ischaemic heart disease (IHD) and coronary risk factors in a defined population using data from all public providers of health care, i.e. inpatient and outpatient care in all settings.

Study Design: Cross-sectional, 1-year retrospective study.

Methods: The main outcome measures were the number of individuals by diagnosis and by care setting, and gender- and age-specific event rates by diagnosis.

Results: Less than half of the individuals who visited any care provider for IHD or coronary risk factors were identified in the hospital discharge register. Calculation of the actual burden of disease in the population showed that when hospital discharge data were combined with outpatient data, there were no or slight differences in the age-specific rates of acute myocardial infarction (AMI), while the rates of angina were between two-fold and four-fold higher, and unspecified IHD was between three-fold and ten-fold higher in individuals aged > or =50 years compared with using hospital discharge data alone. The rates of hypertension, diabetes and lipid disorders increased in all age groups when outpatient data were added to hospital discharge data. The differences in the rates were more pronounced in women aged 50-79 years. However, the age-specific rates were higher in men except for hypertension which was higher in older women.

Conclusion: Data for epidemiological analyses of diseases are often based on hospital discharge data. This study found that hospital discharge data provide limited information on patients treated for IHD and coronary risk factors, except for AMI. These findings suggest that hospital discharge data should be combined with outpatient care data to provide a more comprehensive estimate of the burden of IHD and its risk factors.