When Radio Buttons and Check Boxes are unchecked their value is "Off", so if you have "Yes", "No" buttons you will also encounter an 'Off" value. Now if you want to look at a given button, you will have to use the "isBoxChecked(nWidget)" method.
The 0-based index of an individual radiobutton or checkbox widget for this field. The index is determined by the order in which the individual widgets of this field were created (and is unaffected by tab-order).
Every entry in the Fields panel has a suffix giving this index, for example MyField #0.
true if the specified widget is currently checked, false otherwise.
var f = this.getField("ChkBox");
app.alert("The Box is Checked");
app.alert("The Box is not Checked");