ABSTRACT
In order to produce results that inform a health technology assessment (HTA), a model design must be converted into executable computer code that performs the required calculations. Implementation refers to the actual processes involved in taking the model from design to working software. A discrete event simulation (DES) can, in principle, be constructed using paper and pencil. But apart from its didactic benefit, this is extremely cumbersome even for a very simple model and not feasible for a realistic HTA. Fortunately, the advent of computers made it possible to carry out complex DES, and, thus, since the 1950s there has been very active development of specialized software for DES (see Chapter 9), with many options available today (Greasley 2008; Schriber et al. 2013; Tewoldeberhan et al. 2002). In addition to dedicated simulation software, it is also possible to use general programming languages (Blunk and Fischer 2014; Garrido 2013; Nutaro 2011). This requires, of course, manually coding many of the procedures that are provided as ready-built tools in DES software, but some feel that the gain in flexibility is worthwhile. A third option is to try to use spreadsheet software (Greasley 1998; Klein and Reinhardt 2012; Seppanen 1998). While this appeals to many in the HTA field because of the ubiquitous availability of the programs and the feeling of familiarity with their workings, the spreadsheet approach to representation of a problem and to calculations does not readily accommodate the longitudinal and complex nature of realistic DES for HTA. Nevertheless, many are willing to try and pointers are given throughout this chapter on how to implement features in spreadsheets.
