<p><strong>Comments</strong></p>

<ol>
<li><p>Your <em>culpa</em> doesn't seem <em>maxima</em> enough!  Knowingly cross-posting...<a href="http://youtu.be/syOatIDhAHY" rel="nofollow noreferrer">Shame!!</a></p></li>
<li><p>I'm guessing you're responding to <a href="https://math.stackexchange.com/questions/882644/neyman-pearson-lemma-doubt-on-the-text-of-the-lemma#comment1821565_882644">this comment on your recent Mathematics question</a>. Do clarify if your <code>ME</code> $\ne$ Mathematics. We may wish to discuss the issue on a per-sister-site basis, and having it arise WRT a different site than usual could make this question unique. As is, it might be a dupe of "<a href="https://stats.meta.stackexchange.com/q/1948/32036">Cross-posting in CV and math.SE tends to become an epidemic</a>", but it can't be closed as such for lack of an upvoted answer over there. I also like that you've emphasized the <em>why-nots</em> and <em>what-ifs</em> over the <em>what-should-we-do-abouts</em>; I have much more to say about these. BTW, your question also reincarnates <a href="https://stats.meta.stackexchange.com/questions/1948/cross-posting-in-cv-and-math-se-tends-to-become-an-epidemic?lq=1#comment5354_1948">an upvoted comment on that question</a>, so let's have at it.</p></li>
</ol>

<hr>

<h2>Background</h2>

<p>The more I look into this cross-posting issue is the more it seems controversial to me, rather than clear-cut like <a href="https://stats.stackexchange.com/help/on-topic">the help page</a> suggests:</p>

<blockquote>
  <p>Please note, however, that <em>cross-posting is not encouraged</em> on SE sites. Choose one best location to post your question. Later, if it proves better suited on another site, it can be <em>migrated</em>.</p>
</blockquote>

<p>On that side of the fence, there's also a big fat $\mathbf{NO}$ sitting atop the accepted answer to the <a href="/questions/tagged/faq" class="post-tag moderator-tag" title="show questions tagged &#39;faq&#39;" rel="tag">faq</a>, "<a href="https://meta.stackexchange.com/q/64068/246931">Is cross-posting a question on multiple Stack Exchange sites permitted if the question is on-topic for each site?</a>" Further down, <a href="https://meta.stackexchange.com/a/64073/246931">the second-most upvoted answer</a> is a slippery slope argument against cross-posts by SE's own <a href="https://meta.stackexchange.com/users/1/jeff-atwood">Jeff Atwood</a> <sup><sub>(self-appointed <a href="http://www.codinghorror.com/blog/archives/001169.html" rel="nofollow noreferrer">Stack Overflow Valued Associate #00001</a>)</sub></sup>.
Here on CV, our very own <a href="https://stats.meta.stackexchange.com/users/88/mbq">mbq♦</a> even posted <a href="https://stats.meta.stackexchange.com/a/897/32036">the biggest "<strong><em>NO</em></strong>" you'll find on the network!</a> Looks clear-cut, <em>no?</em></p>

<p>Well...<em>no</em> – look a little further. On the above questions, highly upvoted comments challenge both <a href="https://meta.stackexchange.com/questions/64068/is-cross-posting-a-question-on-multiple-stack-exchange-sites-permitted-if-the-qu/75012#comment302240_64069">the objectivity of the accepted answer</a> and <a href="https://meta.stackexchange.com/questions/64068/is-cross-posting-a-question-on-multiple-stack-exchange-sites-permitted-if-the-qu/75012#comment429638_64073">the slipperiness of the slope</a>. Below, two newer answers argue that <a href="https://meta.stackexchange.com/a/75012/246931">there are exceptions and good practices for them</a>, and <a href="https://meta.stackexchange.com/a/234946/246931">there are systemic incentives</a>. The former has <a href="https://meta.stackexchange.com/questions/64068/is-cross-posting-a-question-on-multiple-stack-exchange-sites-permitted-if-the-qu/234946#comment181805_75012">a supportive comment from Jeff</a> that draws a clearer line between bad and good (or at least <em>acceptable</em>) cross-posting; it has plenty of upvotes too. The latter answer was brief and rather unconvincing (which is an ill-fated approach to arguing against dominant opinion), but it has my upvote – there certainly are wide disparities in site traffic, and I've now edited in a graph to demonstrate just how wide and provided supporting arguments. These include mention of a worthy <a href="/questions/tagged/feature-request" class="post-tag required-tag" title="show questions tagged &#39;feature-request&#39;" rel="tag">feature-request</a> <a href="https://meta.stackexchange.com/q/199989/246931">on MSE</a> with <a href="https://meta.stackexchange.com/questions/199989/build-and-strengthen-the-stack-exchange-community-with-crossover-questions-bet#comment636099_199989">comments linking many others</a>, and <a href="https://meta.stackexchange.com/a/64996/246931">a similar suggestion for good cross-posting practices</a> made by <a href="https://meta.stackexchange.com/users/811/shog9">Shog9</a> (a <a href="http://blog.stackoverflow.com/2011/03/welcome-valued-associate-josh-heyer/">SE Community Manager</a> and <a href="http://stackexchange.com/leagues/4/alltime/meta">kind of a big deal on MSE</a>, second only to Jeff there). Internally, <a href="https://meta.stackexchange.com/users/98786/robert-cartaino">Robert Cartaino</a> <sup><sub>(Director of Community Development and <a href="http://blog.stackoverflow.com/2010/04/welcome-stack-overflow-valued-associate-00005/">Valued Associate #00005</a>)</sup></sub> has also been around longer, and he has also <a href="https://meta.stackexchange.com/a/4713/246931">supported cross-posting in "edge cases"</a>, which I think are losing their "edge" as the network grows and more sites overlap more naturally. On <a href="https://meta.stackexchange.com/q/131950/246931">yet another popular feature request</a>, another MSE <a href="http://www.urbandictionary.com/define.php?term=OG" rel="nofollow noreferrer">OG</a> <a href="https://meta.stackexchange.com/users/102937/robert-harvey">Robert Harvey</a> echoes <a href="https://meta.stackexchange.com/a/212725/246931">the conditional and informal nature of cross-posting policy</a>. CV also expresses dissent on the topic: "<a href="https://stats.meta.stackexchange.com/q/1880/32036">Is the help &#39;misinformed&#39; on the question of cross-posting?</a>"</p>

<p>Hence I wonder if the illusion of clear-cut policy isn't a relic of Jeff's original design that is obsolescing as the network grows in ways that were unforeseeable when these matters were "decided"...</p>

<hr>

<h1>My answer</h1>

<blockquote>
  <p><strong>1) Why should we not cross-post?</strong></p>
</blockquote>

<p>Because you're probably going to <a href="http://knowyourmeme.com/memes/youre-doing-it-wrong" rel="nofollow noreferrer">do it wrong</a> if you haven't thought it through (see background links). That being said, there is <strong>a way to cross-post conscientiously</strong> for questions that deserve it:</p>

<ol>
<li><strong>Read your target sites' on-topic help pages</strong> to check if your question is on-topic at each.</li>
<li><strong>Search the sites' meta-questions</strong> for issues with your question's specific topic (think at the level of specificity that decides what tags to use) and issues of overlap with the other site's main domain. You'll not often be the first to want to cross-post on your particular pair of target sites.</li>
<li><strong>Do not copy-paste; reframe your question.</strong>  Differentiate your two posts to emphasize what aspect(s) of your question you want each community to weigh in on separately. Don't just cross-post to enlarge your audience; do it because each audience may have a different perspective on your problem, and do your part to encourage a different angle of approach on each site.</li>
<li><strong>Link to your other version of the question on the other site.</strong> This facilitates the good side of cross-posting: open juxtaposition of different sets of answers and a bridge between related communities. It also indicates that you're not just thinking of yourself and trying to circumvent the dominant policy thoughtlessly or surreptitiously. Don't underestimate the power of ruffled feathers; tread lightly and respond diplomatically to any critiques from the local leaders. Don't overreact.</li>
</ol>

<blockquote>
  <p><strong>2) What are the possible consequences of persisting in this behaviour?</strong></p>
</blockquote>

<p>This doesn't seem to come up much, which is probably a good thing! I suspect people tend to settle on one site or another depending on which gives the better (or worse) reception, and maybe individuals really don't have that many "edge cases" to offer. I think the collective behavior of the communities persists more, in that new users keep arriving without site preferences, nuanced understanding of sites' topic boundaries, or awareness of the dominant anti-cross-posting policy. This probably fuels that policy's power, because new users tend to ask worse questions anyway*. Hence they probably also take the brunt of that policy's force, for better or worse. They receive more negative feedback at first (call it hazing if you will, but it's purposeful, and ideally, constructive), have more questions closed, and probably suffer a higher incidence of <a href="https://meta.stackexchange.com/q/86997/246931">question bans</a>. I think it must be very rare for people to achieve that level of rejection for cross-posting alone though; truly bad cross-posting is probably comorbid with many other troublesome behaviors that compound to produce that end result.</p>

<p>I suppose if you've "gotten away with it" before, someone might recognize that you're at it again and respond more bluntly or develop an attitude toward you, but it's far wiser to worry about the community's opinion than an individual's. Bringing the issue to the per-site metas (or having it brought there, maybe even in a way that's stilted against you, though we're supposed to keep it impersonal) is the upside of persistence. This is a touchy issue regarding which the whole network needs to work out its ambivalence and resolve its differences. There may be no complete, network-wide solution until a particularly ingenious feature request gets implemented (which could still be a long time from now – it's not gonna be easy), but in the meantime, individual communities can develop local policies and partnerships with their relatives. This is also where we decide what sites to list as migration paths within the flag / close-vote popup dialog. Popular cross-post pairings help inform that decision, because migration is another, softer solution for handling cross-posts that a site doesn't want to keep.</p>

<p>Thus if you feel compelled to persist, bring it up in meta! As you demonstrate, this is one good effect. Of course, if you follow step 2 above, you may also find that others have beaten you to it. Don't forget to vote while you're there! That's ultimately how we steer this thing (to <a href="https://politics.stackexchange.com/a/321/2470">the extent that we do</a> ;).</p>

<hr>

<p><sup><strong>Footnote</strong><br>
* New users asking worse questions, IMO (as a <a href="https://stats.stackexchange.com/help/badges/110/steward?userid=32036">newly badge-holding "steward"</a>!), is due to natural ignorance of <em>many</em> SE policies, the effect of negative feedback from the community that shoos away bad attitudes and incoherent writers early on, and the positive effects of practice for those who persist. We don't just learn the site culture; we learn to communicate! IMO, the effects of this network's feedback are what make it special, and its culture worth accommodating.</sup></p>
