Mortality from ischaemic heart disease in Poland in 1991-1996 estimated by the coding system used since 1997.

BACKGROUND Official statistical data on deaths due to heart disease and cerebrovascular disease in Poland in 1991-2005 are not consistent because of the changes in the coding system introduced after 1996. Between 1996 and 1999, the number of deaths due to ischaemic heart disease (IHD) increased considerably, while the number of deaths due to atherosclerosis decreased. Considering the magnitude of these changes, any analyses of mortality trends in these periods treating these data as consistent are practically impossible. This also applies to international comparisons of IHD mortality data. AIM To develop a method of estimating the number of deaths that would approximate the real numbers of deaths due to IHD in Poland in 1991-2005. METHODS Sets of individual death records from the Central Statistical Office (CSO) and data from the WHO Mortality Database were used. The IHD mortality data documented officially in Poland were obtained using two different coding systems used consistently before and since 1997. IHD mortality was highly consistent in each of these periods. The applied version of the regression model makes use of both these properties. RESULTS The system of certifying death causes which was used in Poland before 1997 resulted in underestimating the real number of IHD deaths in Poland in 1991 by around 35% compared to the numbers estimated using a more correct system of certifying death causes used after 1997. Approximate relative error of the official number of deaths due to IHD in 1991 in age groups of 45-54, 65-74, 75-84, and > or = 85 years was 30%, 24%, 49% and 67%, respectively, in men, and 27%, 25%, 52% and 72%, respectively, in women. CONCLUSIONS An increase in the IHD mortality rate in Poland in 1996-1999 noted by CSO was an apparent phenomenon resulting from inaccuracies in coding death causes before 1997. These inaccuracies were mainly related to IHD, atherosclerosis and cerebrovascular disease. Our method enabled correction of the number of deaths between 1991 and 1996, yielding figures much closer to the real ones. Using this method, it is also possible to assess long-term mortality trends, including evaluation of the effectiveness of different methods of treatment and prevention. In particular, it also refers to the use of the IMPACT model to analyse reasons of changes in IHD mortality in Poland.