<p>If it is really two sentences within a longer answer, it should be OK. No need to paraphrase yourself every time for what is actually a citation. </p>

<p>But having known similar situation on other sites, I would suggest a different approach instead: self-answered canonical questions. </p>

<p>These are really useful when there is a confusing concept which novices often get wrong. For example, let's say that somebody comes with a very concrete problem about a t-test, and you help him straighten his calculation, but also notice that he has no good reason to assume equal variances. So at the end of the answer, you also advise to choose a different test instead, and remember that this is a situation which crops up every now and then. </p>

<p>You can of course reuse some nice explanation you have written as a part of another concrete problem. But you can also write a question, "How do I know if I can use a t-test" and write up an answer which gives a good background about why you shouldn't use a t-test when the variances are unequal, when is it OK to assume equal variances, and what to do if you cannot assume them. Then link from your concrete answer to this well-packaged bit of basic knowledge whenever you need. </p>

<p>This strategy has its drawbacks of course, and is not the one to be used in all cases. Sometimes copy-pasting the couple of sentences <em>is</em> the better thing to do. But keep in mind this alternative too, it can be very fruitful. </p>
