[Coding problems in German mortality statistics as illustrated by ischaemic heart disease]

The German mortality statistics are an important data source in terms of research and health policy but might be influenced by different sources of error such as ICD-10 coding by regional authorities. The aim of this study was to identify state-specific coding problems using the example of ischaemic heart disease (IHD) and myocardial infarction (MI).

After obtaining age-standardised mortality rates (1998-2008), outlier analyses were used to identify German states with suspect changes in mortality from IHD or MI over time or suspect proportional mortality from an unspecific cause-of-death (ICD-10 R00-R99). Values outside the 3-fold interquartile range (IQR) from the IQR boundaries were considered as outliers. The impact of these discrepancies was studied by using an ecological correlation between state-specific poverty rates and mortality from IHD or MI as an example.

During the study period, mortality rates dropped by 38.1% for IHD and by 38.7% for MI. Suspect mortality trends or proportional mortality rates were identified in Berlin, Bremen, Hamburg, Schleswig-Holstein and Saarland. The association between state-specific poverty rates and mortality from IHD or MI increased after exclusion of the suspect states.

The ICD-10 coding by regional authorities seems to be an important source of error. A standardisation of coding procedures is urgently needed.