How widespread is the "back it up" principle?

Question

Good Subjective, Bad Subjective refers to the Back It Up principle that was developed on an early SE site. I've seen this principle in use on UX (though I can't find an example right now), and citing sources or experience is standard on Mi Yodeya.

Backing up an answer includes citing sources, making a logical argument, and sharing relevant personal experience. The idea is to show your work rather than to simply assert something as true.

How widespread is the Back It Up principle on other sites where "compile it and see if it works" doesn't apply? Can answerers, err, please back up answers with links to these policies where they exist?

Edit: While I appreciate (and have upvoted) the answers received so far, I am still hoping for a comprehensive list. I understand from the answers and comments that Gaming, Skeptics, SF, and Workplace have forms this policy; who else, and what shape does it take for each? Ideally one answer would list and link as many of them as possible.

Answer 1

This list was initially compiled from other answers and comments. I'm making it community wiki; please update so we can have one comprehensive list. Please add links to the places where these expectations are spelled out.

The following sites have some form of a back-it-up guideline/policy/rule:

• Skeptics
• Science Fiction and Fantasy
• The Workplace
• English Language and Usage (is this still the case? that post is kind of old)
• UX
• Hinduism
• Christianity
• Islam
• Politics
• History of Science and Mathematics
• Role-playing Games
• Interpersonal Skills
• Software Recommendations

The following sites don't have this as an official rule but operate in a way that strongly encourages the practice:

• Mi Yodeya
• Board and Card Games
• Gaming
• Pets

Answer 2

Some sites would do better with a variation of this principle that is not always supported by the post notices sometimes used by moderators enforcing the back-it-up approach. Travel comes immediately to mind. If you ask about lineups at a particular attraction, the likelihood that a cabbie will be able to give you change from a large bill, or the cleanliness of a particular hotel, which answer would you prefer?

I was there last week and [anecdote]

or

According to Wikipedia [link], [statistical fact which may be out of date, or official position which does not reflect reality on the ground]

One answer on Travel once got one of those "please cite sources" banners:

This post does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed

I flagged asking to have it removed, which it was. Great idea for some sites, but remember we do have some where recent personal experience (for some questions anyway) is actually better than a published, verfied, and possibly out of date or unrealistic "fact".

I'm not saying the plural of anecdote is data. I am saying for some sites, anecdotes are the one thing we can't find from a web search and they are more valuable than data. So if we are to have a system-wide "back it up" principle, and if moderators are likely to use this post-notice on answers that aren't backing it up, we need to either have different post notices (one like the above, and one more pesonal-experience-friendly) for different sites, or two post notices and the moderators choose the right one for the site.

Answer 3

It varies from site to site. The most strict site is probably Skeptics, which requires a citation for almost every statement or claim that is not common knowledge. But it applies to a greater or lesser degree on almost every site. Even Science Fiction and Fantasy encourages references.

Answer 4

We have a "back it up" rule on The Workplace. From the site's FAQ:

How should I answer?

Make sure your answer adds helpful information and is a complete, stand-alone answer. Read other answers first and be sure not to completely restate information that has already been posted.

Please note that answers should be backed up either with a reference, or experiences that happened to you personally. You should always include in your answer information about why you think your answer is correct.

Speaking as a relatively high rep user on the site, the rule has been reasonably successful. Relevant Meta discussions:

• Does this site need a “back it up” rule?
• Should we add a “Back It Up” rule to the FAQ now?
• FAQ proposal: Back It Up and Don't Repeat Others

There's an on-going Meta discussion on Politics to create a similar policy.

Answer 5

On Board and Card Games, it's not an official policy, but it is strongly encouraged (by the way people vote) for all questions, but particularly for rules questions. I'd sum it up as "the community prefers hard evidence, where available, but will settle for logical analysis otherwise". Opinion answers are acceptable, but they are definitely rarer.

As a mod, I do leave gentle comments encouraging evidence when people provide rulings without backup. Quoting the relevant portion of the rules (and linking to them, if available online) seems to me to be the minimal acceptable work here, if you want someone to trust your answer.

The 'show your work' concept seems like a no-brainer to me. Why should anyone value your answer if you can't provide any justification for its existence?