<p>If you search for "one tail" or "one sided", there are tons of hits. Glancing quickly, most of them really are about interpreting or choosing one-sided (one-tailed) tests. I think a tag would be helpful. </p>

<p>What about "Two sided" and "two tails". Another tag? Or make the tag more general: "One vs. two sided tests"??</p>

<p>I'm not sure if this is the right way to propose a new tag, but others have done so in meta, and I can't see an alternative.</p>
