Defining Objectives

With a basic understanding of the system operation and an awareness of the issues of concern or interest, one or more objectives can be defined for the study. Simulation should only be used if an objective can be clearly stated and it is determined that simulation is the most suitable tool for achieving the objective. Defining an objective does not necessarily mean that there needs to be a problem to solve. A perfectly valid objective may be to see if there are, in fact, any unforeseen problems. Common types of objectives for a simulation study include the following:

• Performance Analysis How well does the system perform under a given set of circumstances in all measures of significance (utilization, throughput, waiting times, etc.)?

• Capacity Analysis What is the maximum processing or production capacity of the system?

• Capability Analysis Is the system capable of meeting specific performance requirements (throughput, waiting times, etc.), and, if not, what changes (added resources or improved methods) are recommended for making it capable?

• Comparison Study How well does one system configuration or design variation perform compared to another?

• Sensitivity Analysis Which decision variables are the most influential on one or more performance measures, and how influential are they?

• Optimization Study What combination of feasible values for a given set of decision variables best achieves desired performance objectives?

• Decision/Response Analysis What are the relationships between the values of one or more decision variables and the system response to those changes?

• Constraint Analysis Where are the constraints or bottlenecks in the system and what are workable solutions for either reducing or eliminating those constraints?

• Communication Effectiveness What variables and graphic representations can be used to most effectively depict the dynamic behavior or operation of the system?

Defining the objective should take into account what the ultimate intended use of the model will be. Some models are built as "throw-away" models to be used only once and then discarded. Other models are built to be used on an ongoing basis for continued "what-if" analyses. Some models need only provide a quantitative answer. Others require realistic animation to convince a skeptical customer. Some models are intended for use by only the analyst. Other models are intended for use by managers with little simulation background and must be easy to use. Some models are used to make decisions of minor consequence. Other models are relied upon to make major financial decisions.

Realizing the objectives of a simulation, you should consider both the purpose as well as the intended use of the model. The following questions should be asked when defining the objectives of the study:

• Why is the simulation being performed?

• Who will be using the model?

• To whom will the results of the simulation be presented?

• What information is expected from the model?

• Is this a "throw-away" model?

• How important is the decision being made?