How to show two options without preferring one over the other
The answer really depends on what you are trying to achieve by not expressing a preference. IMHO, there seem to be two takes on this.
1. We are a sensitive company, and want to avoid social bias or discrimination
If so, the issue in the first instance is not due to the choice of UI widget (radio button, select list, or three-position toggles). It is the fact that all the examples use "Male/Female" sequencing, which is conventional but not unbiased.
Most English speakers are naturally more comfortable with Male/Female than Female/Male. Is that gender bias? Most definitely, but in English there is perhaps also a phonetic issue. Even when silently reading, you may stumble as you scan Female/Male since the transition to the bilabial nasal of the "m" of male is uncomfortable whether you say "fe-male-an-d-male","fe-male-or-male" or "fe-male-male". Note that many languages don't have the same phonetic problem e.g. Chinese: nán/nǚ (男/女).
Combining the recommendations of others, I'd suggest that if the object is to avoid disriminatory presentation of sensitive questions like gender, race or religion, there are perhaps four things to consider (regardless of which UI control to use):
- present the selection with an order whose logic derives from a neutral attribute of the options e.g. alphabetical
- ensure full representation of all valid options, to avoid selection bias
- provide an opt-out/other for those who find the question too sensitive or intrusive
- don't pre-select any option
2. It's a Data Quality issue
i.e. people are providing dud answers, and we suspect the order of presentation is a factor.
How do we know if this is a real issue? The best way is to test it e.g. run A/B tests for a sampling of respondents to investigate if there is a statistically significant variation that can only be explained by answer order.
For objective/factual questions like gender, it is hard to understand how order alone can explain or fix a problem with "wrong" answers. It is much more likely that the root cause is either:
- I don't understand the question,
- I don't understand why you are asking or need to know, and I might even be intentionally answering incorrectly
- It's more effort for me to answer correctly than any payoff I think I'll get
For subjective questions, answer order may again be a minor factor amongst many. For example, ask "Who is your favourite team?", and answers may be even more skewed by the color scheme of the page, especially if you are also showing team colors inline.