9. Discrete event simulation (DES)

DES is an individual level simulation approach where individuals interact with the system through a series of events, which may be resource constrained (Robinson, 2018). Within resource-constrained DES queues can build up due to insufficient resources within the system, which can lead to long wait times. For health economic modelling, it is generally assumed that it would be feasible to implement interventions within the current system, with no additional physical resource requirements (Karnon et al., 2012). However, this may not always be the case, and limited resources within a system could affect individual behaviour and outcomes. For example, patients may decide not to utilise stop smoking services because the wait time is too long, particularly if they are less motivated to quit. Decision makers may want to evaluate the impacts of changing the physical resources, for example greater access to stop smoking services. Human behavioural theory could be used within a DES to model the staff which constrain the system (for example, staff may have long periods of sickness absence due to overwork which could lead to longer waiting lists and more overwork), or the individuals who use the system (for example, patients’ previous screening attendance may be a good predictor of future screening attendance). Thus, DES has advantages over other approaches for incorporating the influences on behaviour when behaviour and outcomes are influenced by physical resource constraints.

Currently, very few health economic DES models have been developed which incorporate behavioural theory (Brailsford et al., 2012). There are lots of software options for DES, most of which provide a visual interface which are helpful for sharing with stakeholders. DES requires information about timing of key events in the system, including arrival times, and quantity of constrained resources. Personal characteristics and psychological variables which would affect behaviour and outcomes of the people within the system would also ideally be incorporated.