  Simulation is a well established what-if scenario analysis tool in
Operational Research (OR). While traditionally Discrete Event Simulation (DES)
and System Dynamics Simulation (SDS) are the predominant simulation techniques
in OR, a new simulation technique, namely Agent-Based Simulation (ABS), has
emerged and is gaining more attention. In our research we focus on discrete
simulation methods (i.e. DES and ABS). The contribution made by this paper is
the comparison of DES and combined DES/ABS for modelling human reactive and
different level of detail of human proactive behaviour in service systems. The
results of our experiments show that the level of proactiveness considered in
the model has a big impact on the simulation output. However, there is not a
big difference between the results from the DES and the combined DES/ABS
simulation models. Therefore, for service systems of the type we investigated
we would suggest to use DES as the preferred analysis tool.
