<h1>No, we should not encourage on-topic posts to be posted elsewhere.</h1>
<p>We both agree with this statement.</p>
<blockquote>
<p>Reinforcement learning (RL) is on-topic here.</p>
</blockquote>
<p>Being on-topic means that RL questions can be posted here; there's no reason to send the question away.</p>
<p>By proposing that RL questions are on-topic here on the one hand, but should be encouraged to go elsewhere on the other hand, OP is suggesting some kind of a middle-ground between &quot;on-topic&quot; and &quot;off-topic.&quot; This is harmful, because the disposition of those posts is ambiguous.</p>
<ul>
<li>RL posts shouldn't be closed as off-topic (they're on-topic).</li>
<li>RL posts need not be migrated (they're on-topic here).</li>
<li>OP could <em>request</em> the post be migrated, for instance if the question draws little interest after some time. (But we already have a mechanism to do that: OP flags a post, and it's migrated if that's suitable.)</li>
</ul>
<p>The only mechanism to &quot;encourage&quot; a user that they should post elsewhere is to leave a comment on the post to that effect. But this is confusing, because the comment will give the asker the impression that their RL question is not on-topic here, when, in truth, it is on-topic.</p>
<p>The SE ecosystem works differently from the rest of the Internet, and this difference is counterintuitive to new users. I don't think that adding this additional obstacle to users asking questions is productive or welcoming.</p>
<hr />
<h1>New SE sites shouldn't cannibalize old ones.</h1>
<p>I support creating new SE websites which extend the usage of the SE software to new topic areas. However, the arrival of the AI.SE website overlaps with stats.SE. This isn't <em>necessarily</em> a problem -- two websites can cover the same topic and coexist. But I think it goes too far to attempt to annex a topic from another website just because one site thinks it's a better home for a topic.</p>
<p><a href="https://stackoverflow.blog/2010/10/01/an-area-51-apology-and-clarification/">The SE blog has written about this phenomenon in the past</a>.</p>
<blockquote>
<p>Area 51 was always envisioned as a tool for broadening our scope — for creating new sites serving new topics and answering questions that were previously considered off-topic on our existing sites. Area 51 was never intended as a tool for creating overlapping sub-sites that would cannibalize users from our existing sites!</p>
</blockquote>
<p>The problem of site overlap could have been avoided. A hypothetical Area 51 proposal for a website about the philosophical and conceptual components of AI could have been written. If this proposal excludes statistical topics in AI, this website would not overlap with stats.SE.</p>
<p>But now we're in a place where AI.SE has a topic that <em>does</em> overlap with stat.SE.</p>
<hr />
<h1>OP's reasoning is not sound.</h1>
<blockquote>
<p>However, Stats SE, as we all know, is more statistics-oriented, so there are users here that have no interest in RL</p>
</blockquote>
<p>The observation that some topics are not interesting to all users doesn't change the scope of Stats.SE. If we accept this as a standard for determining scope, stats.SE would be fragmented into time-series.SE, clustering.SE, boosting.SE and so on whenever some number of users became uninterested in other on-topic material. This harms users, because expertise will be scattered across a number of sites. Narrowly-construed website topics also create ambiguity about where to put questions that straddle two domains.</p>
<p>To some extent, this is already happening because the Area 51 process allows the creation of new sites that have large overlap with existing sites. This is baffling, but not really something we, as users of stats.SE, can solve.</p>
<p>I also think that having a broad topic area is beneficial. I've read numerous posts outside of my research area, coursework and professional duties. If stats.SE were a more narrow community, I would be worse off because I wouldn't have the benefit of reading these posts from thoughtful contributors. And it's often happened that I can read a post that I come back to when I need to learn about that topic some years later.</p>
<blockquote>
<p>AI SE has the highest number of questions tagged with RL among AI SE, Stats SE, and Data Science SE.</p>
</blockquote>
<p>The observation that other SE websites have a larger or smaller number of posts about RL doesn't change the scope of Stats.SE.</p>
<p>Moreover, there is a &quot;branding&quot; effect at work. &quot;Artificial intelligence&quot; is a hot topic with a lot of buzz, especially in the popular press. A few years ago, the popular press conferred similar buzz to &quot;big data&quot; and &quot;machine learning.&quot; A user with no knowledge of the SE ecosystem might end up at AI.SE to ask a question simply because of the site's name, even if their question already has an answer on stats.SE.</p>
<p>I don't think that counting tags is sufficient to establish where a question is on-topic. AI.SE also includes philosophical questions about the nature of intelligence among its topics, whereas such questions would be off-topic on stats.SE. Because the union of philosophical questions about RL and quantitative questions about RL must be at least as large as quantitative questions about RL on their own, a simple count of tags on two websites is not making an apples-to-apples comparison between the sites.</p>
<p>On the other hand, the logic of counting tags cuts both ways. Clearly, there are large segments of AI.SE which are squarely on-topic here. Stats.SE has far more <a href="https://stats.stackexchange.com/questions/tagged/machine-learning" class="post-tag" title="show questions tagged &#39;machine-learning&#39;" rel="tag">machine-learning</a> posts (~16,000 on stats.SE versus ~1700 on AI.SE), and probably similarly for several related topics. Should we divert AI.SE users who ask about machine learning to stats.SE? I don't think this makes sense, but it's the inevitable conclusion if we make topic decisions based on tag counts. And I doubt that the AI.SE community would want to part with a core topic in artificial intelligence.</p>
<p>Finally, the occurrence of more RL tags on AI.SE could stem, at least in part, from a particular user's unilateral effort to leave comments discourage RL questions from being posted on stats.SE.</p>
<blockquote>
<p>I've personally noticed that many people interested in RL end up on AI SE and they regularly visit the site, and this includes people that answer RL questions even on Stats SE and Data Science SE</p>
</blockquote>
<p>The same users having accounts across one or more of the quantitative fora doesn't change the scope of stats.SE. Probability and statistics questions regularly show up on math.SE; some of them are answered by users who also post to stats.SE. This doesn't change what is topical on math.SE, nor does it change what is topical here.</p>
<blockquote>
<p>Although it's true that both AI SE, Stats SE, and Data Science SE are &quot;competing&quot; for users, wouldn't the 3 (overlapping) communities benefit from having a more solid collaboration? I think so.</p>
</blockquote>
<p>The communities are not competing for users. Membership or participation in one community doesn't preclude membership or participation in another. I simply don't grant the premise of the question.</p>
<p>The word &quot;collaboration&quot; suggests people working together towards a common goal. What is the common goal that you have in mind here?</p>
<h1>The core problem is <em>fragmentation</em>, which we can't stop.</h1>
<p>To my mind, the goal of stats.SE is to answer statistical questions (broadly conceived). Fragmenting the statistical field (to include data science, machine learning and AI) across multiple websites seems to work against that goal, and does not promote it.</p>
<ul>
<li><p>Fragmenting the field across an archipelago of quantitative websites makes it more difficult for new and existing users to make use of these websites because they will have to know the exact, arcane delineations between each site's scope.</p>
</li>
<li><p>Fragmentation makes it harder to find answers, because you have to search in multiple places. To some extent, general purpose search engines (Google, Yahoo!, Bing) can help, but SE has unique search tools for searching within a specific site. I've found these tools are very helpful, but they only search one SE site at a time.</p>
</li>
<li><p>Fragmentation creates duplicated effort. The same question can be asked and answered in 2 places.</p>
</li>
</ul>
<p>I appreciate that fragmentation is happening already, but it is unresolvable as long as there are SE websites with overlapping content. Because we both agree that RL is on-topic here, there's simply no reason to send on-topic posts elsewhere. On-topic posts are on-topic.</p>
<p>I think it's useful to consider this question from the perspective of <em>minimizing site overlap</em>.  A Venn diagram of AI.SE, DS.SE and stats.SE has a lot of overlap, so if the problem we seek to solve is reducing fragmentation, does AI.SE need to exist as a distinct website?</p>
<p>Or, since there is an interest in philosophical questions about intelligent agents, should AI.SE's scope be narrowed to only include questions which are not topical on stats.SE? This solves the problem of topic overlap, while retaining all of the unique content and expertise at AI.SE.</p>
<p>I'm not trying to pick a fight with the AI.SE folks by asking these provocative question, so please don't read it that way. I am trying to tease out what the core issue is. The answers to these questions will provide a better understanding of how to approach topic overlap and mitigate the problems stemming from it.</p>
<p>To me, the root of this problem is that questions about what is on-topic will persists as long as there are multiple, overlapping websites with very similar topics, but with fine-grained distinctions.</p>
<h1>Users can choose where to ask their questions.</h1>
<p>A user might want to ask about building a fence. This user has a number of places they might ask such a question.</p>
<ul>
<li><p>They could ask on DIY.SE to learn about construction methods or get materials recommendations.</p>
</li>
<li><p>They could ask on law.SE to learn about potential legal entanglements, such as legal risks arising from a contractor getting injured on their property while building the fence, or the consequences of annexing some of their neighbor's property due to a surveying error.</p>
</li>
<li><p>They could have a question about how to construct the shape of the fence so that a tethered goat grazes over a specific area. (<a href="https://www.quantamagazine.org/mathematician-solves-centuries-old-grazing-goat-problem-exactly-20201209/" rel="nofollow noreferrer">This example is inspired by an old mathematical puzzle.</a>)</p>
</li>
</ul>
<p>I think users' choices are important to keep in mind, because the decision to post in one place but not another place is a deliberate decision by the user to seek help from a particular community. (Sometimes a user asks an off-topic question, but we both agree RL questions are on-topic.)</p>
<p>What tag-counting <em>does</em> tell us is that users have tended to ask their RL questions on AI.SE. To me, this suggests that the only thing we need to do for AI.SE to continue to attract RL questions is for AI.SE to continue to provide high-quality answers, a task that AI.SE is doing very well today.</p>
