Routinely collected health administrative data has become an important data source for investigators assessing disease epidemiology. The aim of this study was to investigate the implications of identifying acute coronary syndrome (ACS) events in New Zealand national hospitalisation data using either the first (primary) or subsequent (secondary) codes.

https://www.researchgate.net/publication/342513702_The_Importance_of_Considering_Both_Primary_and_Secondary_Diagnostic_Codes_When_Using_Administrative_Health_Data_to_Study_Acute_Coronary_Syndrome_Epidemiology_ANZACS-QI_47