<p>They key to understanding difficult is in realizing that the results of any standardized test is scaled (ETS calls it “equating”). That means they determine the score by looking at the results of all the people who took it. Simply put, if any test was easier than the other, they adjust the scales so they always get the same distribution. </p>
<p>Any practice test from barrons cant be accurately scaled because it was never given to a large audience. The blue book is the only source that gives you that. </p>
<p>That being said I dont think their is a huge difference between all these tests. If you want a good predictor of your score, use blue book. If you just want a bunch of questions to study with barrons is fine.</p>