Adaptive test scores are based on the difficulty of the questions you answer correctly and incorrectly not on the number of questions answered correctly. In other words, the score is based on the difficulty levels of the questions you can answer correctly, rather than simply on the number of questions you answered correctly. Novell uses an ability score scale that has a minimum value near 200 and a maximum value near 800. All test scores will fall somewhere on this scale. You will pass the test if your score is equal to or greater than the cutoff score.
All tests have a similar passing rate.
From that perspective one test is no harder than any other. However, it takes a great deal of preparation, even over-preparation, to pass them. Most certification candidates have learned this fact and are obviously putting forth the necessary effort. Once the test has obtained an accurate score, the test stops. If the test taker has not obtained a passing score after 25 questions, the test stops.