Informal methods of validation and verification are some of the more frequently used in modeling and simulation. They are called informal because they are more qualitative than quantitative. While many methods of validation or verification rely on numerical results, informal methods tend to rely on the opinions of experts to draw a conclusion. While numerical results are not the primary focus, this does not mean that the numerical results are completely ignored. There are several reasons why an informal method might be chosen. In some cases, informal methods offer the convenience of quick testing to see if a model can be validated. In other instances, informal methods are simply the best available option. Informal methods are not less effective than formal methods and should be performed with the same discipline and structure that one would expect in "formal" methods. When executed properly, solid conclusions can be made.
In modeling and simulation, verification techniques are used to analyze the state of the model. Verification is completed by different methods with the focus of comparing different aspects of the executable model with the conceptual model. On the other hand, validation methods are the methods by which a model, either conceptual or executable is compared with the situation it is trying to model. Both are methods by which the model can be analyzed to help find defects in the modeling methods being used, or potential misrepresentations of the real-life situation.
Inspection
Inspection is a verification method that is used to compare how correctly the conceptual model matches the executable model. Teams of experts, developers, and testers will thoroughly scan the content (algorithms, programming code, documents, equations) in the original conceptual model and compare with the appropriate counterpart to verify how closely the executable model matches. One of the main purposes of this method of verification is to see what original goals have been overlooked. By doing an inspection check on the model, the team can not only see what issues might have been overlooked, but also catch any potential flaws that can become an issue later in the project.
Depending on the resources available, the members of the inspection team may or may not be part of the model production team. Preferably they would be separate groups, but when members are from the same group aspects may be overlooked since the group members have already spent time looking at the project from a production point of view. Inspections are also more flexible in that they may be ad hoc or highly structured, with members of an inspection team assigned specific roles such as moderator, reader, and recorder, and specific procedure steps used in the inspection. The inspectors' goal is to find and document flaws between the conceptual model and the executable model.
Face validation
One of the benefits of face validation is that it can effectively be used during a real-time virtual simulation where the interaction between the user and the simulation is of priority. It is effective during these type of simulations because these types of models require input or interaction from the user. The best way to validate that the model meets the criteria is by having users who have experienced the model situation in real life confirm that the model accurately represents the situation they are familiar with. Users who are familiar with the situation will notice necessary corrections that a developer may be unaware of. This type of validation is effective and most appropriate for virtual simulations and it is also used to validate models when there is a short timeframe scheduled for testing, or when it is difficult to produce quantitative results that can be analyzed. While quantitative results should be the preferred result, a solid account of validation from professionals is also acceptable.
Examples of face validation
The accuracy of a flight simulator's response to control inputs can be evaluated by having an experienced pilot fly the simulator through a range of maneuvers. Analyzing the accuracy of a poker bot simulator's response to user input to verify that the A.I. is reacting in a logical manner. Having a soldier test a model that simulates a battle situation.
Audit
An audit is used to establish how well a model matches the guidelines that are set in place. If an audit trail is in place, any error in the model should be able to be traced back to the original source to easily find and make corrections. An audit is conducted by meetings and following the audit trail to check for issues.