Oct 8, 2011

How does GMAT scoring algorithm actually works?

Disclaimer: Knowing specifically how the GMAT is scored won’t help your score much (if at all), so if you only have a few hours left to study please study! Really, the only way to improve your score is to get more questions right.

Often students wonder about the scoring system when they see the same scores (e.g., two people who each score 49 Quant and 35 Verbal) correspond to two different overall scores (e.g., those same two people earning 690 and 700), or they improve their scaled scores and don’t see a significant increase in their overall (e.g., improving from 50Q and 31V to 49Q and 35V, but the increase is only from 690 to 700). What’s going on?
Dr. Larry Rudner of GMAC recently addressed these issues at last month’s GMAT Summit for top test preparation companies. Here’s what we learned from his presentation:
  • The 200-800 score is the final report, sent to schools to stay consistent with the old paper-and-pencil (pre-1997) test scoring system, but the scoring algorithm used in the computer uses its own system and just converts the 0-60 and 200-800 values over as that last step in reporting.
  • Each scaled score has a corresponding “interim range” (or, actually, the interim range is what the computer first gives you before converting to a scaled score) which spans 2-3 numerical values, so your 50 on Quant might correspond to a range of 60-62 on that GMAT computer scale (again, the computer uses its own numbers that are more consistent with how the CAT algorithm scores you, then the system converts to the familiar display numbers). Those interim scores for Quant and verbal are then combined and your “interim sum” (which now may span 5-6 potential values since you’re adding two ranges together) is then converted to your 200-800 score.

    So not all 49s (scaled score) are created equal — your 49 might be a “high 49″ (at the higher end of the interim range of scores and someone else’s might be a “low 49.” When the computer uses its interim value, if you have a high/high split of interim values for the same Q/V scaled scores and someone else has a low/low split on theirs, your 49/39 might be a 730 and theirs a 710. The 3-digit 200-800 score is valid — it’s just that you don’t see the full process that goes into calculating it.
  • So as an example (courtesy Dr. Rudner’s presentation), if you have a 50Q/31V, that has a potential range of:

    – Quant: 51 scaled –> 60-62 interim range (you could be a 60 or a 62 and still end up at 51 scaled)
    – Verbal: 31 scaled –> 42-43 interim range

    Total: 102 – 105 on the interim scale, on which 102 would correspond to a 670 and 105 would correspond to a 690. So the same two scaled scores could swing 20 points either way on the overall score, and that’s because the overall score is calculated using the computer’s numbers, not your score report numbers.

However complicated, the system is quite transparent; you can learn more about it at www.mba.com, the Graduate Management Admissions Council’s site for statistical research and trends. You’ll see there that your score is calculated fairly, accurately, and efficiently. So, as always, the lesson is to worry less about how your score is measured and more about how to maximize the value of that measurement!

by - VeritasPrep


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