Hey,
I'm not so sure that the difference in your scores is due to the difficulty levels of the practice tests. While
Manhattan GMAT practice tests aren't official, we try to mimic the official test algorithm as closely as possible. Your higher scores are probably due to an increase in your ability level over the past couple months. Looks like all your hard work is paying off!
For the official test, GMAC has published a "within student" standard deviation of 30 points, and GMATPrep is supposed to be about the same. A "within student" SD means that if the student takes the test a bunch of times in a row (without studying / learning more in between), the standard deviation of that student's scores will be about 30.
We (
MGMAT) have done extensive analysis of our large pool of students and their practice and official test scores.
The "within student" SD is about 50 points on our tests. The "last
MGMAT test to official test" SD is also about 50 points.
Every 2 months, we calibrate our scoring algorithm to ensure that our test, on average (across all students now) is an unbiased estimator of GMAT performance. What this means: some students do better on the official test and some students do worse (compared to last
MGMAT test). When we look at performance across all of our students, we attempt to ensure that the average difference balances out to zero. In practice, we ensure that the average difference in last
MGMAT test score vs. official test score is between +5 and -5 points across all students. What this means: our tests do not consistently under- or over-estimate scores.
Best,
Matt Mapplebeck
Student Services Associate
Manhattan GMAT