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Weird GMATPrep scoring question

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Weird GMATPrep scoring question

by thassan » Wed Jul 03, 2013 9:06 am
Hi All, quick, general GMAT question. I have read that the GMAT's adaptive nature tries to align difficulty of questions to the test taker's ability such that the test taker gets ~50% correct. Oddly, I took the official GMATPrep exam and got only 14/37 quant questions incorrect, about 38%. Why didn't the exam give me harder questions? Does it have to do with the fact that I ended on a streak of 8 correct? Another important fact worth mentioning is that I didn't get a particularly high score on the quant - right around 50th percentile, actually. This tells me that there were harder questions I could have gotten?

Also, a slightly unrelated questions, I am assuming the GMATPrep software does not mimic the exact functionality of the GMAT - correct? If it did, wouldn't smarter people than me be able to look up the code that determines the scoring / questions selection algorithm and reveal the secret? Is that what's driving the odd results?

IMO, 38% is far enough away from 50% to be weird.


Which of the following best explain the discrepancy? Just kidding, no answer choices :)
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by Brent@GMATPrepNow » Thu Jul 04, 2013 6:14 am
I believe that the algorithm typically results in students getting 50 - 60% correct, so your 62% seems reasonable.
Why didn't the exam give me harder questions?
The most likely answer is that the questions you previously answered incorrectly were quite easy, so the algorithm "decided" to send your easier questions.
I am assuming the GMATPrep software does not mimic the exact functionality of the GMAT - correct? If it did, wouldn't smarter people than me be able to look up the code that determines the scoring / questions selection algorithm and reveal the secret?
The algorithm used in the GMATPrep practice tests is the same as the algorithm used in the real test.
The test-makers have created an algorithm that cannot be exploited in any significant way. If you correctly answer difficult questions, you get more difficult questions, and this results in a higher score.

The most important thing to understand about the algorithm is that your scores are not based on how many questions you answer correctly; they're based on the level of difficulty of the questions you answer correctly. To illustrate this, I'll share an experiment I performed:

I took GMATPrep Practice Test #1 four times, and each time I answered every second question correctly (I did this for the quant section only). Given that I correctly answered exactly half of the questions each time, you'd expect my quant scores to be roughly the same for all 4 tests.

My 4 scaled scores were: 19, 23, 26 and 42

This represents a percentile range from approximately 8th percentile to the 63rd percentile.

From this huge range of scores, I can only conclude that there were times when I incorrectly answered several easy questions, and there were times when I correctly answered several difficult questions.

Takeaway: Don't search for secrets hidden in the algorithm. Your goal should be to answer each question correctly.

Aside: If anyone is interested, we have a free video explaining the GMAT scoring algorithm: https://www.gmatprepnow.com/module/gener ... es?id=1251

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by David@VeritasPrep » Fri Jul 05, 2013 6:17 pm
Brent has explained many things already. I just want to note that getting 23 questions right/ 14 wrong does not tell the story. It matters which 23 questions. For example, people get about 25 questions right and score anywhere from below the 60th percentile to above around the 90th percentile.

Yes the test is seeking to eventually find your level, but this does not mean that you will get 50% of questions right. Perhaps if there were 1000 questions that would be true, but 37 questions is not enough for the test to determine your level and give you mostly questions at that level!!

Do not worry about anything in the scoring except this:

1) If you can get a question right in a reasonable amount of time focus and get it right.

2) If you are not making progress on a question consider guessing and moving on.

Your ONLY task on the GMAT is to get questions right. You cannot control anything other than that. Get the questions right that you can get right and the score will take care of itself.
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