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. Because radio buttons require exactly one choice, make sure that the options are both comprehensive and clearly distinct. In tests with older users, for example, people couldn't complete a form that required them to select their job because it didn't offer "retired" as an option. If it's impossible to be comprehensive, offer a button labeled "Other," supplemented by a type-in field. Checkboxes vs. Radio Buttons by Jakob Nielsenon September 27, 2004 https://www.nngroup.com/articles/checkboxes-vs-radio-buttons/ (出典)