Should our default gender when selecting male/female on the dropdown list be based on the local sex ratio (if a country have more female than male then female is the default value)?
You don't select a default at all
Using a drop down list or a radio group - you let the user decide - and this also prevents accidental submission of a form without the user setting this value (assuming it's gets validated) because there is no other way of validating it - only the user knows their gender so there is no right/wrong validation other than 'is it set'
Here are examples from Windows Live ID sign-up, Facebook sign-up, Yahoo sign-up
In fact in my own survey of over 100 high profile sign-up forms:
Only 20% of those sites asked the gender of which:
- 20 did not pre-select - by using one of the options above.
- 2 forms prefilled with the option 'Female' (bebo and foursquare)
- 0 forms prefilled with 'Male'
Furthermore - of the 20 that did not pre-select:
Grooveshark go the extra mile (although I'd at least expect consistency)
- to try and make it clearer by using symbols on their sign up:
- or in their 'edit profile' they use another version in which the wording has clearly been carefully considered and accounts for the gender/sex issue as to how the user identifies themselves:
How about asking the user to select their gender in the form of their preferred third-person pronoun ("his", "her", "their"), instead of providing their biological sex?
Listing "their" rather than "its", because I doubt anyone wants to be referred to as "it". For example:
Which sentence sounds right? [ ] <user> updated his profile. [ ] <user> updated her profile. [ ] <user> updated their profile.
Unless you have a good reason to have the gender, I would agree with @Roger that not pre-selecting is the best option. I would also add that not validating at all, and allowing a selection of Male and Female is probably the best option.
The clientelle of the site is also important, and not always obvious. Females are far more common users of web sites - especially e-commerce - than are normally expected. Knowing your users is critical if you insist on setting a default - many of the sites I have worked on, female would be default.
In form fields like that, I usually make the first value null, to indicate no item was selected.
As far as order, I would either defer to the audience, then just go standard M/F
For the drop down, make it optional, with the default value of null (so as to allow form submission without error)
Gender: Select one <null> Male <male> Female <female>
If the system is asking about biology, simply asking "Sex: Male / Female", without a default, is absolutely the best option.
If the system is asking about something else, including all this stuff about "queers" that I am seeing in conversation, then ask a different question.
If you make sure to ask the right question, your data scientists will thank you.