# Contents

# Question

How does BayesiaLab calculate the Means and Values in the **Monitors**? What is the difference?

# Answer

This *Expected Value* is displayed in the monitor.

**Example**

Let's take a discrete node *Age* with three categorical states:

- Young Adult
- Adult
- Senior

The **Node Editor** allows associating numerical values with these states.

Let's suppose now that the variable *Age* has three numerical states.

As it's a numerical node, its monitor will have a *Mean* value, a *Standard Deviation* and an *Expected Value*.

Otherwise, the state values defined by the user are used:

Let's consider now a continuous variable *Age* defined on the domain [15 ; 99], discretized into three states:

- Young Adult: [15 ; 30]
- Adult: ]30 ; 60]
- Senior: ]60 ; 99]

Since it's a numerical node, its monitor has a *Mean* value, a* Standard Deviation* and an *Expected Value *as well.

- the mid-range of the state when no data is associated,
- the arithmetic mean of the data points that are associated with the state.

When new pieces of evidence are set, a the delta value is displayed in the monitor:

This delta is the difference between the current *Expected Value v*

and:

- the previous one,
- the one corresponding to the reference probability distribution set with in the toolbar.