Radiobutton group with NO default option: bug / acceptable / it depends?

Question

I'd like to have an independent opinion / samples of whether radiobutton group should have an option selected by default: some colleagues tend to submit missing choice as an issue, while others say this is OK. However, I think there are several samples where NO default choice seems to be fine:

Please select your age:
( ) 16-20
( ) 21-25
( ) 26-30
( ) 31-40
( ) 41-50
( ) 50+

From where I sit it looks like for that case NO default selection is fine, otherwise some users may left that option unchanged, while it may be especially important according to business logic.

One more option is sorting: ASC / DESC choice, while at the same time no sorting is still acceptable by application / business logic.

To be more specific and not to make this a discussion, please provide specific samples where default choice is obligatory, and where it is NOT.

Answer 1

There are at least two (conflicting) ways to think about this:

Whether you provide a default depends on the context. If you provide a default, you should be prepared for people to select it even when it's the wrong selection. This is particularly true for user interfaces that require lots of inputs.

For example, my company's application has an online calculator for determining how much money the government will permit them to contribute to their health savings account. The contribution amount depends on whether the employee's health insurance covers just the employee or their entire family. If the employee contributes too much, they will need to go through a tedious process to "undo" their excess contributions. The online calculator asks the employee to specify what kind of health insurance they have. The calculator used to provide a default value, and people tended to use that value without thinking about whether it was appropriate. Eventually we decided to remove the default.

On the other hand, there are times when a default is appropriate. If the default choice is the most likely or the best choice under the circumstances, you can improve usability by saving the user the trouble of selecting that value. This is especially true if the cost of changing your mind later is low. For example, imagine a website for viewing movie trailers. You can view the movie in three different resolutions. The lowest resolutions will download the fastest, which saves money for the website owner, and possibly saves money for the user, too. The cost of switching is low, and the website owner knows that most people prefer to use the lowest resolution, so it makes sense to default to the lowest resolution.

You need a hard-and-fast rule because consistency improves usability. Consistency (always selecting a default radio button, or never selecting a default radio button) leads to fewer surprises, and an object is more usable when you know what to expect out of it.

Answer 2

In actuality, the usability issues only come into play in a very specific case. In most cases, providing a default for a radio button list is actually a straightforward logic issue. Here are all of the parameters I can think of (in order of precedence):

Is the user required to provide a choice?

If no, then a default selection should never be displayed.

If yes, then

Is a "non-choice" selection provided?

If yes, then select this option by default.

If no, then is there an overriding reason for highlighting -or- requiring the user to actively answer the question?

If yes, then do not provide a default selection. In your example, if this is an online employment application for working at a location serving alcohol, then not providing a default choice and having the question highlighted in bold, red, and asterisked with a note that the question is required would be appropriate (assuming the first selection would reject them outright).

If no, then we finally get into usability issues where the answer becomes a choice based on context, clarity, and consistency.