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GMAT Prep Software Analysis and What If Scenarios

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 06 Sep 2014, 05:46
I hope we all are assuming rightly that GMATPREP and original test have the same logic.

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 15 Sep 2014, 09:19
Thank you Bunuel and Vercules for this great thorough Analysis!!!!
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New post 15 Sep 2014, 17:30
Amazing people (Bunuel and Vercules) have done some amazing work....thanks for sharing such valuable information here....1000+ kudos to both of you for leading such monumental task...

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 23 Oct 2014, 06:33
Its one of the best article i did gone through here in GMAT Club.
A big thanks to Bunnel and all the others who have contributed to this analysis. :o
Although i am looking more forward for verbal analysis.

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 23 Oct 2014, 08:18
Can anybody share whether they experienced similar results on the actual GMAT test?

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 23 Oct 2014, 09:29
p2bhokie wrote:
Can anybody share whether they experienced similar results on the actual GMAT test?



This is the only report I have: 600-to-740-all-about-timing-and-fundamentals-147029.html
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New post 23 Oct 2014, 12:53
Thanks bb. The post that Manish has written is very informative. I am sweating bullets since My D-day is coming up quickly. Thanks for taking time to post Manish's debrief.

Posted from my mobile device

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 08 Nov 2014, 14:16
Would someone well versed on this thread mind succinctly recapping the results of the trials? I'm scanning through, but it's a little hard to synthesize it all. Thanks and best.

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 09 Nov 2014, 10:35
Dear Bunuel ,

Did you try leaving the last 8 or 10 questions for verbal ?
I tried & I was surprised to see that the penalty for leaving verbal is insignificant. Can you please confirm with your analysis ?

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New post 16 Mar 2015, 22:39
Nice post...Very Insightful...thanks everyone!
I am kinda new on the forum, so I don't know if this is the right place for asking this: Regardless in what part of the test, do I get more punished for getting a sequence of wrong questions versus getting the same number of wrong questions, but randomly ?
I mean comparing: 4 right + 6 wrong (random) vs. 4 right + 6 wrong (in a sequence)
If there is a difference I would say it would be maximized if this happened on the first 10.
Thanks again everyone

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 08 May 2015, 11:04
These kinds of GMATPrep experiments are fine, but it's extremely easy to arrive at incorrect conclusions from them, unless you understand how the scoring algorithm works. Some of the conclusions drawn in this thread are not correct, though in some cases it will take me some time to explain why. I'll try to do so over a few posts in the coming days. For example, here:

Vercules wrote:

Analysis/ Conclusion :



Results from 15 tests show that on average an Option 'C' carries a higher probability of being correct and option B carries the lowest. ...

But if you have to guess one or two and you have no idea/ time for the question mark 'C'.


There is a GMAC research report which explicitly states that they control for 'answer position' when designing the GMAT. That is, no one answer choice is right more often than another. I've also verified that independently; looking over more than 1000 official questions, each answer choice is correct roughly equally often.

That said, if you look only at a small sample of questions, one answer choice might appear to be correct more often than another, just because of random variance. If you do a binomial probability calculation, then if each answer choice has a 20% chance to be correct on a random GMAT question, it would not be all that improbable for one answer choice to be correct 13 times on one GMAT Quant test (that should happen on about 2% of tests). Since your samples do not appear to be independent (I assume you were using the same GMATPrep test repeatedly, in which case it would not be surprising to get similar results each time because of question repetition), the most likely explanation for your findings is pure random luck.

But if instead you assume that your finding is meaningful, and that, when guessing randomly at every question, C is the most likely answer to be correct, what would that finding mean? It might seem paradoxical, but it means that test takers who need to guess almost certainly should not guess C. If you accept (and all the evidence I have confirms this) that each answer is correct about 20% of the time, then if C is the right answer more often when you guess at every question, that means C is more often the right answer on the absolute easiest questions. For C then to be correct 20% of the time overall, C would need to be correct less often on the harder questions. And those are the questions people need to guess at.

Even if you don't believe each answer is right 20% of the time, knowing which answer is more often correct on 200-level questions is of no help to test takers unless they'll need to guess at 200-level questions, which almost no one needs to do. So it would not be a relevant finding for most test takers anyway. But all of the evidence I've seen suggests to me that no one answer choice is a better guess than another, if you need to guess purely at random. The best strategy in that case is simply to guess as quickly as possible.
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To understand the meaning of other experiments in this thread, it's important to understand how the scoring algorithm works. There are really two parts to the algorithm:

• the actual scoring algorithm, which determines your score based on your answers
• the question selection algorithm, which determines, based on your previous answers, which question you see next

The scoring algorithm itself is completely blind to question position. If you were to take a GMAT, and all 37 questions were 500-level, you'd get exactly the same score by answering the first 25 correctly and the last 12 incorrectly as you'd get by answering the first 12 incorrectly and the last 25 correctly. The scoring algorithm itself knows nothing about where each question was in the test; it's simply not a factor in the calculation.

What does change, though, based on your answers, are the questions you see later in the test. When you do well early on, you'll more likely see hard questions later, and if you do badly early on, you'll more likely see easy questions. Note though that every test is different. If you answer, say, your first five questions correctly (which is outstanding). The test will then be quite confident you're a high-level test taker, and will want to give you a very hard question. But your ability estimate is not the only factor the test uses to select your next question. The test also needs to meet content requirements (more than one - it needs to deliver the correct balance of math topics, and also the correct balance of PS and DS questions), and there are security conditions as well (no question is used too often, in order to prevent people from getting a big advantage by learning about test questions in advance of the test). The question database is not enormous for a single test, which means that, if you get your first 5 questions right, while the test might want to make your sixth question a 760-level question, there may not be a question exactly at that level that meets all of the conditions the test needs to meet. So depending on the database on the day you take your test, you might get a 700-level question at that point, or an 800-level question.

So every test is different, which is why you'll get different results each time when you carry out experiments where you get questions in certain positions wrong (every odd numbered question, say). I have the impression that the assumption behind those experiments is that questions are 'weighted' by their position in the test (that early questions count more than later ones), and that's not the case.

To demonstrate this, I did just carry out two trials using two different GMATPrep Quant tests, where I answered every prime numbered question (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37) incorrectly. On the first attempt, my score was Q33, and on the second, it was Q38. That's quite a big difference.

I'm not precisely sure what the purpose of these experiments is, testing how wrong answers in different places will affect your score, but if the goal is to find certain question numbers that are especially important or unimportant, you simply won't be able to do that. It's not how the test works.
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New post 28 May 2015, 00:41
This post is Great!!

Thanks for sharing such valuable information here
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New post 08 Jun 2015, 10:27
That was very thoughtful of you Bunuel and Vercules!

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 08 Jun 2015, 11:40
Great thanks to Bunuel and Vercules for this analysis. This is really helpful for understanding value of first 10 questions.

But I found some strange results in my two GMAT prep exams.

In the first exam I make 4 mistakes in first 10 questions and 11 wrong questions in common but received 50 scores
And second exam was much better: 2 errors in first 10 questions and 8 wrong question in common but received only 49

Looks like first 3-4 question play even more significant role than first 10 questions.
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New post 09 Jun 2015, 10:53
A surprising turn of events. In the Official GMAT Monthly this was featured in their FAQ section:

Q: Are the practice GMAT tests on the software indicative of how well you'll do on the actual GMAT?
A: GMATPrep® software uses real GMAT test questions and the actual GMAT CAT® test delivery and scoring algorithm. It should help you to gauge your preparedness for the GMAT exam. Note - the predictive value of these tests may be affected by the extent to which actual testing conditions are adhered to during practice testing sessions. For example, if you were to suspend testing and resume the test later, an option that you have with GMATPrep software but not with the actual GMAT CAT exam, you might score higher on GMATPrep test than you would otherwise.


Previously it was stated/believed that the GMAT Prep and GMAT used different algorithms (a more simplified algorithm was used in GMAT Prep)
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New post 09 Jun 2015, 17:34
bb wrote:

Previously it was stated/believed that the GMAT Prep and GMAT used different algorithms (a more simplified algorithm was used in GMAT Prep)


I'm almost certain it is not true, and never has been true, that GMATPrep used a different basic scoring algorithm from the real test. I've never heard any official statement that would make me think otherwise, and if there has been one, I'd love to see a link.

The fundamental scoring algorithm used in GMATPrep really has to be the same as is used in the actual GMAT, because the scoring is just based on probability theory, and GMAC isn't free to change the laws of math. There are differences between GMATPrep and the GMAT (for example, GMATPrep does not insert experimental questions in the way the real test does), but those differences don't have to do with the actual scoring of the test.Those differences almost certainly still exist, so I don't think this recent announcement is new information, or signals any change in the GMATPrep tests.
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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 23 Jun 2015, 08:56
I just did a GMAT Prep exam (from Exam Pack 1). Got the first 4 questions wrong - and then no string of 2 incorrect answers in a row.

Scored a 31!, like.. really? That big of an impact?

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New post 12 Jul 2015, 06:43
What would be the outcome if every 3rd question in Verbal is incorrect? (for ex- ques no 3,6,9 and so forth...)

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Re: GMAT Prep Software Analysis and What If Scenarios [#permalink]

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New post 19 Jul 2015, 00:00
bb wrote:
A surprising turn of events. In the Official GMAT Monthly this was featured in their FAQ section:

Q: Are the practice GMAT tests on the software indicative of how well you'll do on the actual GMAT?
A: GMATPrep® software uses real GMAT test questions and the actual GMAT CAT® test delivery and scoring algorithm. It should help you to gauge your preparedness for the GMAT exam. Note - the predictive value of these tests may be affected by the extent to which actual testing conditions are adhered to during practice testing sessions. For example, if you were to suspend testing and resume the test later, an option that you have with GMATPrep software but not with the actual GMAT CAT exam, you might score higher on GMATPrep test than you would otherwise.


Previously it was stated/believed that the GMAT Prep and GMAT used different algorithms (a more simplified algorithm was used in GMAT Prep)


I got something contradictory here.
I got Q48 on GMAT prep exam pack-1 and I did only 6 questions wrong.
The questions wrong were 2,17,24,26,28,33.
Is it possible? Or there is some problem with the logic because I did test 4 first and then test 3, and I got Q49 with 9 wrong questions in test 3. Or is it like i had no or very few good(700level) questions left in question bank so test gave me 600-700 level questions and I got Q-48 only.
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Re: GMAT Prep Software Analysis and What If Scenarios   [#permalink] 19 Jul 2015, 00:00

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