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
To store an observation as an Evidence Scenario, click the
icon.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.
Now, an additional icon
in the Status Bar indicates that there is an Evidence Scenario File.
Right-clicking the
icon in the Status Bar brings up the list of stored Evidence Scenarios, enumerated by an index and, if available, with corresponding comments. You can add further Evidence Scenarios to the ones already stored in the internal Evidence Scenario File.
So, the next time to click the
icon, the pop-up window asks whether you want to append the new Evidence Scenario to the list of Evidence Scenarios or replace a particular existing Evidence Scenario.
To apply (or recall) a stored Evidence Scenario, right-click on the Evidence Scenario File icon
in the Status Bar and click on the scenario you want to apply to the network.
Also, hovering over the Evidence Scenario File icon
with your pointer brings up the number of available Evidence Scenarios.
Upon selecting (and therefore applying) an Evidence Scenario, the corresponding comment, if available, appears in the Status Bar.
You can remove the current Evidence Scenario File by left-clicking on the
icon. 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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