Evidence Scenario File

Context

  • In BayesiaLab, you can manage sets of actual or potential observations in a Bayesian network using Evidence Scenario Files.

  • For instance, an Evidence Scenario File can serve as a convenient way to manage multiple sets of assumptions, such as what-if scenarios. This is particularly helpful when scenarios contain many individual assumptions. Imagine the business case of an airline represented as a Bayesian network. It would have to include assumptions regarding travel demand for all origin-destination pairs. Manually setting and modifying assumptions for hundreds of nodes would not be practical.

Definition

  • An Evidence Scenario File consists of one or more Evidence Scenarios.

  • And, each Evidence Scenario contains one or more node-specific observations, as illustrated below:

  • Applying an Evidence Scenario means setting the stored pieces of evidence to the corresponding nodes.

Note that evidence cannot be set on Not Observable Nodes, i.e., nodes that have a Cost of 0 (see Cost Management).

Store Evidence Scenarios in Validation Mode

With a given Bayesian network, any current observation on a node or sets of observations set on multiple nodes can be recorded as an Evidence Scenario. As soon as you store an Evidence Scenario, BayesiaLab "starts a tab" by creating an internal Evidence Scenario File.

Four types of evidence can be saved as an Evidence Scenario:

  • Hard Evidence

  • Likelihood Evidence

  • Probabilistic Evidence

  • Numerical Evidence

To learn more about setting evidence, please see the section on Setting Evidence in Contextual Menu of Monitors.

Usage

  • Then, enter an optional comment in the pop-up window and assign a Weight to the Evidence Scenario you are storing. If you don't enter a comment, the Evidence Scenario will merely be indexed sequentially, starting with 0.

  • Click OK to confirm.

  • You can add further Evidence Scenarios to the ones already stored in the internal Evidence Scenario File.

  • Upon selecting (and therefore applying) an Evidence Scenario, the corresponding comment, if available, appears in the Status Bar.

  • Note that an Evidence Scenario File is saved with the Bayesian network file. So, reopening the saved network makes all stored Evidence Scenarios available again.

Inference with an Evidence Scenario File

In addition to recalling Evidence Scenarios one by one, you can also use them in BayesiaLab batch-processing functions:

  • Batch Labeling

  • Batch Inference

  • Batch Joint Probability

  • Batch Outlier Explanation

In this context, the Evidence Scenario File provides the observations in the same way as an internal or external dataset.

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