by ayang Wed Mar 21, 2007 11:09 am
Alok,
It has been the case that students have scored similarly to you on the MGMAT CAT and had strong, but not stellar results on the actual GMAT.
We’ve been monitoring the scoring closely. So far, our data is showing that the highest score a student gets on one of our practice tests overshoots the score on the real GMAT by about 10-15 points. We haven’t yet made an adjustment to the algorithm because we haven’t yet confirmed this is statistically significant. We are looking to make an adjustment, though, as soon as we can confirm the level of the inflation.
The standard deviation of the difference (between the practice test score and the real GMAT score) is 50-60 points. We would like to reduce this and are taking steps to do so, but note that for many reasons, a practice test can never perfectly predict the GMAT. For one thing, the GMAT itself has a standard error of 29 points - meaning that only 2/3 of the time would you expect to get within ~30 points of your "real" score. Also, we write simulated questions and use a simulated algorithm - neither of which can we calibrate perfectly to the real GMAT. Finally, YOU are a big variable. When a student takes a practice test - even the GMATPrep, which does use the real algorithm and real questions - the student knows that it’s practice. The fact that the real GMAT counts is a factor that no practice test can simulate, naturally.
Our algorithm mimics the algorithm of the real GMAT but is not exactly the same, true. GMATPrep does use the real algorithm, but the pool of questions does not seem to be anywhere as deep as that of the real GMAT. The practical effect of this "shallowness" of the pool is that high performance deviates more from the theoretical 50-60% right that pure IRT (item response theory, the theory behind the algorithm of the GMAT which we understand quite well) would predict. In simpler terms, if the pool is shallow, the algorithm cannot give you "tough enough" questions while still meeting the constraints of content breadth and format breadth. Thus you would expect to get more right on a shallow-pool GMATPrep than you would on the deep-pool real GMAT. Our pool is deeper, which leads to a closer fit to the 50-60% right that pure IRT predicts.
We will continue to invest time and resources into perfecting our algorithm and our question pool. We believe we already have the best test out there besides the GMAT Prep (which of course uses real questions & the real algorithm), but we won’t rest on our laurels.
All that said - the actual score is the least important piece of information from any practice test. You should neither be elated by a high practice test score nor deflated by a low one. You should use practice tests to do two things: (1) identify relative strengths and weaknesses, and (2) gain experience with the format of the test.
The takeaway - the fact that you got a 780 on the CAT is a great sign, but you should not take it as indicative of what you'll score on the real GMAT beyond the fact that you're performing very well on our practice test. Continue to do your best to identify relative weaknesses in preparation for the real test. The only perfect data remains the real GMAT itself.
I hope that this is helpful to you. Let me know if we can provide any other info or assistance. All of the best, - Andrew