# Defining a variable as a distribution

To define a variable as an Analytica probability distribution, first select the variable and open either the variable’s **Object window** or the **Attribute panel** of the diagram with **Definition** selected from the **Attribute** popup menu.

To define the distribution:

- Click the
menu above the definition field and select**expr****Distribution**.

- The
**Object Finder**opens, showing the Distribution library.

- Select the distribution you wish to use.
- Enter the values for the parameters. You can use an expression or refer to other variables by name in the parameter fields.
- Click OK to accept the distribution.

If the parameters of the distribution are single numbers, a button appears with the name of the distribution, indicating that the variable is defined as a distribution. To edit the parameters, click this button.

If the parameters of the distribution are complex expressions, the distribution displays as an expression. For example:

`Normal((Price/Mpy)*Mpg, Mpg/10)`

**Entering a distribution as an expression**

Alternatively, you can directly enter a distribution as an expression:

- Set the cursor in the definition field and type in the distribution name and parameters, for example -
*Normal(.105, 0.015)* - Press
*Alt-Enter*or click thebutton.

You can also paste a distribution from the Distribution library in the **Definition** menu (see Using a library).

You can edit a distribution as an expression, whether it was entered as a distribution from the Distribution library or as an expression, by selecting **expr** from the **expr** menu.

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