Recently I encountered a business requirement whereby it was stipulated that both radio buttons in a group be left unchecked. In addition to this, a check was required to forcing the user to select one before they can continue.
This struck me as being direct contradiction as to what a Radio button was trying to achieve, and that it was actually more work as you were forcing the user to make a choice without giving them a default.
It just felt wrong.
But I wasn’t sure, so I did a bit of research, and came up with the following.
Firstly (and some could say, lastly) there is the W3 Recommendation at http://www.w3.org/TR/html401/interact/forms.html#radio:
At all times, exactly one of the radio buttons in a set is checked.
And that ought to be it, but for completeness, here is quite a nice set of guidelines regarding this http://www.useit.com/alertbox/20040927.html:
Always offer a default selection for radio button lists. By definition, radio buttons always have exactly one option selected, and you therefore shouldn’t display them without a default selection. (Checkboxes, in contrast, often default to having none of the options selected.)
If users might need to refrain from making a selection, you should provide a radio button for this choice, such as one labeled “None.” Offering users an explicit, neutral option to click is better than requiring the implicit act of not selecting from the list, especially because doing the latter violates the rule of always having exactly one option chosen.
