The development of a data-matching algorithm to define the 'case patient'. 
To describe a model that matches electronic patient care records within a given case to one or more patients within that case.  his retrospective study included data from all metropolitan Ambulance Victoria electronic patient care records (n=445576) for the time period 1 January 2009-31 May 2010.  Data were captured via VACIS (Ambulance Victoria, Melbourne, Vic.,  Australia), an in-field electronic data capture system linked to an integrated data warehouse database.  The case patient algorithm included 'Jaro-Winkler', 'Soundex' and 'weight matching' conditions.  he case patient matching algorithm has a sensitivity of 99.98%, a specificity of 99.91% and an overall accuracy of 99.98%.  The case patient algorithm provides Ambulance Victoria with a sophisticated, efficient and highly accurate method of matching patient records within a given case.  This method has applicability to other emergency services where unique identifiers are case based rather than patient based.