<p>I am happy with your suggestion to create a <code>pre-post-design</code> tag which may be helpful to better identify questions dealing with specific experimental designs. (In passing I noticed we don't even have a tag for <a href="http://www.socialresearchmethods.net/kb/quasiexp.php" rel="nofollow">quasi-experimental designs</a>.)</p>

<p>It seems to me that the <code>repeated-measures</code> tag does not necessarily cover exactly the same topic as it can be associated to longitudinal data, or repeated measurements in designed experiments (e.g., in psychology), to name a few. As such, pre-post design would just belong or be a sub-category of that more general tag. Also, <code>change-scores</code> are more alike 'derived variables', as stated in plain English, while they are also suggestive of a statistical technique for analyzing two-group parallel design, which is <a href="http://biostat.mc.vanderbilt.edu/wiki/Main/MeasureChange" rel="nofollow">not necessarily the way to go</a>.</p>
