Cardiovascular
Differences in cardiovascular disease, mortality in high income countries are too large to be explained by health system quality alone – using the normalized mortality index can help to clear the mist Bernd Kowall* Susanne Stolpe
Background
Age-standardised mortality (ASM) from cardiovascular diseases (CVD), especially from ischemic heart disease (IHD), is used to assess the quality of health systems. IHD mortality in high-income countries is very diverse. In 2019, ASM for IHD in Germany (44.7/100.000) was much higher than in the neighbour countries Netherlands (NL, 18.2/100.000) and Denmark (DK, 23.2), but lower than in the USA (53.9). CVD mortality is affected by national preferences in cause of death (CoD) selection, not necessarily reflecting population morbidity: in 2019, IHD was selected as CoD in NL in 5.4% of all deaths, in DK in 6.2%, but twice as often in DE and USA. Therefore, it is questionable if conclusions on health care quality are reliable.
Aim
To develop a measure to compare disease-specific mortality that more reliably reflects differences without being affected by different preferences in CoD selection.
Methods
WHO data on all deaths, CVD and IHD deaths, and ASMs for CVD and IHD for West-European countries, USA, Australia and Canada for 2019 was used. The normalized mortality index was calculated by dividing the ASM by the proportion of IHD and CVD resp. among all CoD, then multiplying by 10. This normalizes the ASM to reflect a CoD proportion of 10% of all deaths.
Results
The normalized mortality index for IHD in 2019 was similar for NL (33.4), DE (35.3) and DK (37.4), but higher for the USA (42.6) – plausibly indicating comparable or lower (USA) health system quality. For CVD, equally assuming a 10% share as CoD, the normalized mortality index was slightly lower (NL: 30.4, DE: 33.8, DK: 35.8, US: 41.9).
Conclusion
The normalized mortality index is easy to calculate. Normalizing the disease-specific ASM to a proportion of 10% as CoD among all deaths avoids distortions by nationally preferential CoD selection and enables more reliable conclusions on health system quality and population health. We recommend to include the normalized mortality index in health reporting.
