"Neil Drumm" wrote:
From the report: "Binary options should use two radio buttons, one for each of the states."
From Nielson's Alertbox: "A stand-alone checkbox is used for a single option that the user can turn on or off" (http://www.useit.com/alertbox/20040927.html).
These are distinct interface (and logical, more precisely) elements. The first you reference is a 'binary' object group. That is, it is an object that has only 2 states (represented by the buttons in the group), but one of the states is required. The second logical element, the checkbox, is a 2-state object which may be value-less. Often, but not always, 'valueless' is logically equivalent to some other value (say, zero). Therefore, the UI principle to consider to distinguish the two interface elements is: radio button -- when a value is required to be provided checkbox -- when a value is able to be toggled (to the 'no value' state) Again, often but not always logically equivalent. -- inkfree