<p>It's called test equating. ACT gives a basic description of their scoring here: <a href="http://www.act.org/research/briefs/2001-1.html%5B/url%5D">http://www.act.org/research/briefs/2001-1.html</a> Furthermore, the following is taken from <a href="http://www.isbe.state.il.us/high_school/psae_myths.ppt%5B/url%5D">http://www.isbe.state.il.us/high_school/psae_myths.ppt</a></p>
<p>"The test development and equating process is NOT designed to impose a particular distribution of scores on every form. That is, it does not “force” a certain percentage of examinees to get low scores across forms or across test dates."</p>