Glad to read this question here, have often wondered about this myself.
User:Emelian1977, an African American PhD student named Brenton Stewart, conducted a survey of Black American Wikipedians in 2008. I can only find a short write-up of his study online:
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http://webcache.googleusercontent.com/search?q=cache:v_96mBI74-MJ:ocs.sfu.ca...
Paper 2: Working for Free: Motivations Behind Black Contributions to the Wikipedia Project
The dirty little secret of the Internet is that it’s built upon free labor. Internet labor exists in a unique dualism in that the production and reproduction of web and social networking sites as well as the design of some computer games and software are manifest as entertainment, leisure or hobbyist escapism - but not as labor. Greg Downey (2001) argues that this type of “flexible labor is hard to see” noting that “the commodification of the virtual serves to mystify the material.” Few entities in the new digital economy have capitalized upon this form of labour extraction better than the Wikipedia Project, the world’s first peer-produced online encyclopedia. However, Wikipedia’s sole reliance on unpaid laborers means that it reflects the interests and biases of these contributors who are overwhelmingly homogeneous. This study is a descriptive investigation into the factors that influence African American contributions to the Wikipedia project. Situated within Tiziana Terranova’s (2001) social-factory theory this research seeks to understand the role of racial/ethnic identification as a motivator, Wikipedia as a space for the extension of black volunteerism, and the topics most frequently edited by this community of Wikipedians.
The findings suggest that while these Wikipedians contribute as a form of entertainment and support for the democratization of information they are also motivated by their racial/ethnic identity, highly cognizant of their minority status and tended to view their edits (labor) as a transgressive act that is ultimately beneficial to the black community. This research argues the social-factory forms the foundation of not only Wikipedia but also a multitude of online peer-produced communities such as Facebook, MySpace and YouTube. What is most significant about these communities is that their end product, the cultural knowledge of the masses, is freely given and results in enormous revenue for their parent companies. This investigation contributes to diverse literature including media and library & information studies as well as cyber and community activism.
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I'll let that stand there without comment; there are obviously several ways one can look at that.
I know of at least one African American admin on en:WP, but only a handful of other black Wikipedians. A while ago I took part in discussions at [[Ancient Egyptian race controversy]]; my impression was that black editors there were given quite a hard time -- resistance to including works by black scholars, because they were deemed unreliable, etc., the standard POV stuff. I tried to help out for a while, but then got sidetracked.
The influx of Indian editors will be an interesting challenge. I firmly expect that at some point over the next 10 or 20 years, Indian editors will have something like numerical parity with Western editors. At the moment, being in a minority, they have trouble getting their points across.
Look at [[British Empire]] for example, which paints a fairly rosy picture of colonialism which would be considered ridiculously POV in India, or at [[Famine in India]], an article written with a more Indian POV, where some of the same opponents are battling it out. What's NPOV depends on whether you allow Indian sources or stick to Western sources.
On top of it, an en:WP bureaucrat recently blocked an Indian editor in good standing without prior warning and without talk page notice, for 2 weeks, for "trolling and pov pushing at British Empire and talk" (currently at AN/I). Same crat also commented to another admin on their talk page,
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How the WMF sees India as the new goldmine and is making a big din there with speaking tours and likes. More like a goldmine of copyvio, ethnic and religious fundamentalist POV. There will be a flood of dudes like {{User|X}} if their initiative works, which'll be funny. As you can see on the mailing list, which is public, all these leaders are queueing, IPL- style feeding frenzy. X is after me, lol
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The other day, the same crat appeared to call another Indian editor a "retarded nationalist" in an edit summary, never showed up for the resulting AN/I thread, and escaped without any sanction whatsoever.
A few mostly Indian editors have recently argued that the article [[Ganges]] should be renamed [[Ganga]], as that is now the river's official name in India. Now, to be sure, this is not a clearcut case, as Ganges can still be found in a few Indian sources, and the name Ganga is only making slow inroads in Western news reporting -- it does occur a few times, but not that often yet. But one brilliant, tell-tale comment in the discussion was, "When Britain and the USA start using Ganga predominently instead of Ganges, then the article could be changed."
Now, this is India's holy river, and we always go on about how we want to educate kids in poorer countries. But we are telling kids in India that they can't read about their national river in an article that bears the name that is the river's official name in their country. Comments like that, "When Britain and the USA start using Ganga predominently instead of Ganges", are just arrogant and unfortunate, and an extension of the colonial mindset. If the US changed the spelling of Mississippi, I bet that Wikipedia would follow suit the same day, regardless of whether the media in India had caught up with that change or not.
So I think one reason why we don't see more diversity is that the established, predominantly white user base is giving editors from other backgrounds a pretty hard time!
Cheers, Andreas