<p>As it has been psoted before, the curve is predetermined, does anyone know, as CB is constructing a test, and they pick (for a random example here), 7# "5" questions, and say 6 #4 type questions, is it individual questions, or the test as a whole? That a particular form say the DEBM test(again another random example) that previously most kids got questions 15, 16, 17, 18 wrong, so that declares those ?'s #5 question. Or is it from that day of the testing, this particular group of kids majority of the kids get # 15, 16, 17 , 18 wrong, then that makes those #5 questions?</p>
<p>Well, on all of the recent tests that aren't actually administered by CB the difficulties are only e,m, and h. So for tests with 1-5 (which are always previously adminstered) I'm sure there has to be some way of determining the difficulties more specifically. I'm not sure if it is taken from the actual test results or from previous experimental sections or other data.</p>
<p>So I guess it is from past administrations of those particular questions, if I read the pdf correctly.</p>