OptionGroup Object [Access 2003 VBA Language Reference]
An option group on a form or report displays a limited set of alternatives. An option group makes selecting a value easy since you can just click the value you want. Only one option in an option group can be selected at a time.
An option group consists of a group frame and a set of check boxes, toggle buttons, or option buttons.
Note This control should not be confused with the Dynamic HTML option group control used on a data access page. For information about a option group control on a data access page, see Option Group Control (Data Access Pages).
Using the OptionGroup object
If an option group is bound to a field, only the group frame itself is bound to the field, not the check boxes, toggle buttons, or option buttons inside the frame. Instead of setting the ControlSource property for each control in the option group, you set the OptionValue property of each check box, toggle button, or option button to a number that's meaningful for the field to which the group frame is bound. When you select an option in an option group, Microsoft Access sets the value of the field to which the option group is bound to the value of the selected option's OptionValue property.
Note The OptionValue property is set to a number because the value of an option group can only be a number, not text. Microsoft Access stores this number in the underlying table. In the preceding example, if you want to display the name of the shipper instead of a number in the Orders table, you can create a separate table called Shippers that stores shipper names, and then make the ShipVia field in the Orders table afield that looks up data in the Shippers table.
An option group can also be set to an expression, or it can be unbound. You can use an unbound option group in a custom dialog box to accept user input and then carry out an action based on that input.