<p>For an identically difficult test, the curve <em>must</em> change (and become tougher); otherwise, the standardization of the test is lost (i.e., a 4 in 2011 needs to mean the same thing as a 4 in 2010, namely, a “B” grade level of achievement). The percentage of people scoring 5’s (or any other score) will change (more than that associated with random fluctuations) only if the quality of the students taking the test significantly changes.</p>
<p>The two curves published for the same test (eg Euro history) are instructive because they suggest (roughly, at least), the extra number of points that would be expected due to the lack of a guessing penalty.</p>