Interpreting and using GMAT practice tests.

This question comes from a former student:

Doug-

Can you help explain the test scoring for me? The inconsistency in the test scoring is stressing me out. So far I've taken both the Kaplan practice CAT's and the mba.com practice CAT's.

Kaplan Cat3 Q-20 correct V- 17 correct Total 520

Kaplan Cat4 Q-16 correct V- 22 correct Total 500

GMAT prep test 1- Q 18 correct V- 19 Total 510

GMAT prep test 2- Q- 19 correct V- 28 correct Total 490???

As you can see my highest verbal yet and second highest quantitative so my score should be at least higher than a 510-520?? I know the math seems to be weighted higher but their last score doesn't make sense.

Is it possible the program scored me wrong or am I missing something here?

Anything's possible. However, looking at your overall scores, I actually see very little inconsistency. On the other hand, you are focusing on the number of correct answers compared across four tests. To understand the apparent discrepancy, keep in mind two concepts: First, the test is scored on a curve, so your overall (scaled) score depends not only on how you performed, but also on how other test takers scored. Second, and more importantly, remember how the test algorithm works. If you get several questions wrong in the beginning of the test, the algorithm lowers your score and gives you easier questions. After that, you can readily answer more (now easier) questions correctly but will have a tough time recovering on the maximum achievable scaled score. (I'd be curious to know how much variation you noticed in your percentile rankings and scaled scores.)

Your overall scores have been remarkably consistent. GMAC says you can expect your score on test day to be within +/- 40 points of your true ability 2/3 of the time. By contrast, your mean score over the four tests you cited is 505 with a standard deviation of only 13 points.

I've got another opportunity for you to consider. You didn't mention how frequently you've taken these tests. After each practice CAT, are you taking time to review your results question by question and identify areas that need work? You should follow up such an analysis with additional practice before tackling another CAT. Taking practice tests without the supplementary work in between might help you improve your timing (and conceivably raise your score thereby) but it won't generate your maximum performance increase.

You've already boosted your scores by 100 points from the diagnostic test. To maintain your momentum, I suggest that you analyze the tests you've completed so far to figure out which two or three topics, strategies, or concepts offer the biggest potential harvest of points - and then dig in on those areas intensively.

- Doug