Means and Values of Nodes
Context
At the top of each Monitor, the items Mean, Dev, and Value are displayed.
Mean refers to the Mean Value m and is only shown in the Monitors of numerical nodes.
Dev stands for Standard Deviation and is shown alongside Mean.
Examples
The calculations for Expected Value and Mean Value are shown in the context of the following examples:
Categorical Node
Let's take the discrete node Age with three categorical Node States:
Child
Adult
Senior
Categorial Node with Assigned State Values
In the Node Editor, you can assign State Values to the Node States of Age.
A Monitor of a categorical node does not show a Mean value.
Discrete Numerical Variable
Let's suppose that the node Age has three numerical Node States instead of categorical Node States.
In this context, we need to consider two conditions, with and without State Values specified in the Node Editor:
No State Values Specified
Here, State Values are not specified in the Values tab of the Node Editor. Note the empty Value column below.
As a result, BayesiaLab uses the numerical values of the Node States, as they appear in the States tab, as the State Values.
Furthermore, as Age is a numerical node, its Monitor will now display the Mean (Mean) and the Standard Deviation (Dev) in addition to the Expected Value (Value)
The Mean m is computed using the numerical values of the Node States and the marginal probability distribution of the Node States:
Note that Mean and Value are identical in this case.
State Values Specified
However, if State Values are separately specified in the Values tab of the Node Editor, they will be used for the calculation of Value in the Monitor.
To highlight the distinction between the Node States {10, 40, 70} and the State Values, we assign unrelated arbitrary State Values of 0, 1, and 2.
Note that Mean and Value are not identical in this case.
Continuous Numerical Variable
Let's now consider a continuous variable Age defined in the domain [0; 99], discretized into three states:
Child: [0 ; 18]
Adult: ]18 ; 65]
Senior: ]65 ; 99]
Given Age is a numerical node, its Monitor shows the Mean (Mean), the Standard Deviation (Dev), plus the Expected Value (Value).
No Associated Data
So, the Mean Value m is computed as follows:
Associated Data
Value Delta
If you set a new piece of evidence on a node that modifies the distribution of the node, the Monitor displays a delta value in parentheses adjacent to Value.
This delta is the difference between the current Expected Valuev and:
Special Case: Some Node States Without Values
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