David Kuntz developed the algorithm for Knewton’s GMAT prep course, and this is the final installment in his CAT FAQ. For more info, check out part 1 and part 2.

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How can my overall percentile be higher than both my quantitative and verbal percentiles?

Your overall score is calculated separately from your section scores, so you can score in the 99th percentile on the GMAT even if you didn’t score in the 99th percentile on either of the sections. For example, you could get a 48 on Quantitative (86th percentile), a 45 on Verbal (98th percentile), and a 760 overall (99th percentile).

Are the quantitative and verbal sections weighted equally in the total score?

Technically, yes — the estimates of your quantitative and verbal abilities that the CAT produces contribute the same amount to your overall score. However, the verbal section has a greater effect on your percentile rank because it is generally more difficult. If, for example, you scored a 40 on both the Quantitative and Verbal sections, your percentile rank for Quantitative would be 61st, but for Verbal it would be 91st. Your overall score (650) would be in the 84th percentile.

Why are scores above 51 rare? Why does the scale go up to 60? Can anyone get a 52?

For psychometric reasons, GMAC has truncated the scale at 51 (they do not report section scores higher than 51).

Why is it so difficult to create a good CAT?

A CAT needs to do many things well in order to reliably and accurately estimate your ability. It requires a robust algorithm to estimate your ability, a complex but speedy mechanism to identify the best question for you to see next, a rich pool of questions from which to select the questions, and a powerful scoring algorithm that translates the ability estimate into something meaningful. Each test question has many characteristics that need to be simultaneously considered in the selection. The statistical characteristics of the questions all need to be determined beforehand through a process known as pretesting. Many, many questions are needed in order to be able to provide accurate assessment for all ability levels. And all of those questions need to be carefully constructed, reviewed, and statistically aligned so that they contribute meaningfully to your ability estimate.

Rich is one of Knewton’s expert GMAT teachers, but he’s also a whiz at SAT prep.

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Subject-verb agreement is a fairly simple thing we all learn about early in school:  If a subject is singular, the verb must also be singular.  For example, in the sentence “Thomas sells clothing,” the singular noun “Thomas” is matched with the singular verb “sells”.  It can be confusing, of course, that “sells” has an ’s’ at the end (since s’s are often at the end of plural nouns). But because “sells” matches with the singular “Thomas,” it must be singular.

Likewise, a verb will be plural if its subject is plural, as in “The salespeople sell clothing.”  Again, even though the word “sell” may appear to be singular, it is plural because it is matched with the plural “salespeople.”

These are fairly straightforward examples.  But of course, the SAT has to make things a little bit trickier.  Interestingly enough, the SAT Writing section tries to trip you up not by making the content itself more difficult, but by changing the sentence structure so it becomes harder to recognize errors in subject-verb agreement.

Here’s an example of a “find the error” question that does just this:

Did you find the disguised subject-verb agreement error?  If not, try removing the modifying clause in between the two commas, and then read the resulting sentence:  “Music theory help musicians both understand their artform and appreciate its nuances.”

Pretty obvious now, isn’t it?  The singular “Music theory” is incorrectly matched with the plural “help.”  The sentence should of course read, “Music theory… helps musicians…”

Notice that what makes this question “difficult” is in no way related to content.  All they do is throw in a modifying clause between the subject and the verb, increasing the distance between the two for confusion’s sake.

And notice that in this case, the SAT writers double your fun by ending the modifying clause with the plural “ensembles,” which looks pretty good when paired with the next word, the plural “help.”  The problem, of course, is that even though “ensembles” and “help” appear back-to-back in the sentence, they are not paired together in terms of the sentence’s meaning.  “Music theory” is the thing that “helps,” not “ensembles.”

This happens extremely often on the SAT Writing section.  The test will separate the subject from the verb to confuse you, and it will also conclude a modifying clause with a noun that correctly matches the main verb in number but not in terms of the sentence’s meaning.

Be on the lookout for these types of errors as you work through your SAT practice questions!  Knowing this simple trick will help you tackle many questions on test day.

We are pleased to announce the winners of Knewton’s Preppy New Year contest! Hundreds entered, but only four could win a free Knewton GMAT prep or LSAT prep course.

And the winners are:

• Joseph Chung
• Kristin Rohn
• Debbie Icebergsewell
• Ashwini Mishra

Congrats, everyone! For those who didn’t win this time, don’t worry — we have more goodies planned for the very near future.

Fan us on Facebook to stay in the loop!

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photo by Chris_J on Flickr.

Brad McIlquham is Knewton’s Director of Academics. He is really into surveys, but then again, who isn’t?

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The February 2010 LSAT was this past weekend (at least for those who managed to avoid the massive snow cancellations). Just like we did in September and December, we polled our hearty Knewton students to get their feedback on the exam.

Most students who responded were from our full-length LSAT prep course, but a handful were from the first run of our 2-week Total Access program — their study program was abbreviated and largely self-directed, so we were interested to hear their feedback as well.

All told, the majority of respondents (70%) found the Logic Games section to be the most challenging. This majority wasn’t as overwhelming as it was in December — when over 80% agreed that AR was the toughest — but it still dwarfed the next runner-up. Only about 30% found Logical Reasoning to be the most difficult, while close to no respondents thought RC was the hardest.

Full results after the jump:

(more…)

If your LSAT administration was canceled this weekend, you should be getting another email from the LSAC in the next few days; when weather gets in the way of an exam, they try to schedule a make-up test within two to three weeks.

Here are some things you should do if your LSAT was canceled:

• Hang on to your admission ticket; this will get you into the make-up test when it’s scheduled.
• If schools are waiting on your LSAT score, give them a call to explain that your test was delayed.
• Keep practicing! A postponement is disappointing, but it’s a great chance to take a few more practice tests.

For students whose Knewton LSAT prep memberships were set to end last weekend, we’re extending your courses until the make-up exams are finished. Next weekend is a holiday, so chances are most re-tests will be the weekend of February 19th or 26th. In the meantime, keep up the hard work!

Better hurry! Today's your last chance to win a free LSAT or GMAT course.

Our Preppy New Year Contest ends today! If you want to win a free LSAT prep or GMAT prep course (and who wouldn”t!), you have to enter by 6:36pm EST. Just click the contest link, fan us on Facebook, and enter your info. Easy!

Make this the year that you rock the LSAT or GMAT. Good luck!

A storm’s a-brewin’, and the LSAC has already canceled a number of tomorrow’s LSAT administrations. Before you head out tomorrow, check to make sure your test center is open! The LSAC is keeping of running list of centers that are already closed, and that list is sure to grow today and tomorrow.

Here are the closings so far, state by state:

Delaware

Center 1330 – University of Delaware, Newark, DE

Maryland

Center 1364 – Towson University, Towson, MD
Center 1381 – Towson University, Towson, MD (overflow)
Center 1382 – Towson University, Towson, MD (overflow)
Center 1369 – University of Maryland-Eastern Shore, Princess Anne, MD
Center 1371 – University of Maryland-College Park, College Park, MD
Center 1372 – University of Maryland (Overflow)-College Park, College Park, MD
Center 1386 – Montgomery College, Rockville, MD
Center 1393 – Hagerstown Community College, Hagerstown, MD

Ohio

Center 4528 – Cedarville University, Cedarville, OH

Pennsylvania

Center 2012 – Villanova University, Villanova, PA
Center 2019 – Lebanon Valley College, Annville, PA
Center 2025 – Millersville University, Millersville, PA

Virginia

Center 1582 – Washington & Lee University, Lexington, VA
Center 1594 – Hampden-Sydney College, Hampden Sydney, VA
Center 1597 – University of Mary Washington, Fredericksburg, VA
Center 1598 – Northern Virginia Community College, Springfield, VA
Center 1609 – Liberty University, Lynchburg, VA

Washington, DC

Center 1556 – Howard University, Washington, DC
Center 1569 – Catholic University of America, Washington, DC

It can be a drag if your LSAT administration is canceled, but don’t fret. The LSAC will usually contact you with rescheduling information within a week. Silver lining: more time for LSAT prep.

Read more:

What to do if your test center closed

The February LSAT is tomorrow, and it always helps to get a little last-minute advice. Kristen taught a great exam-day seminar back in December, so all you February test-takers should check it out! The link is below, as are some tips to remember once you’re in the exam.

One last thing: It looks like weather may affect a number of test centers tomorrow, and the LSAC has already issued some cancellation notices. Check their site regularly to make sure your test center will still be open.

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For all of you taking the LSAT tomorrow, good luck! By now you’ve done your practice tests, run through your drills, and gotten yourselves in optimal LSAT-taking shape. How should you spend your last precious hours before the test? Here are some tips.

I’m posting a link to a workshop we ran for our Knewton LSAT prep students. Anyone can view it, so check it out! We’ll break down how to approach the writing sample, how to prepare for test day itself, and what you should do for last-minute prep.

To watch the archive video, click here.

A minor note on test-taking strategy. One of the best tricks (and the simplest) is to make sure you have your answer-bubbling strategy in place. There are strategies! You can bubble in answers a question at a time or wait until you finish a page, RC passage, or logic game. All methods work, just choose the one you like best beforehand so you’re consistent.

There’s no penalty for guessing on the LSAT, so also make sure you fill in every answer choice before time runs out. If you have a few minutes at the end of the section, use it to review questions you were unsure about and double-check that you’ve taken a stab at every answer.

Remember that the goal for tomorrow is accumulating points, not achieving perfection. These small tips can lead to big gains over the course of the test.

Good luck everyone!

Kristen

That's right. Venturing into the wide, wide world of Facebook quizzes.

Wondering about what kind of lawyer you would be? This quiz makes it crystal clear. Fair warning: there may be a Johnny Cochran reference.

Once you find your true calling, we’re also happy to help with your LSAT prep. Happy quizzing!

David Kuntz is Vice President, Research at Knewton, where he builds the CATs for its online GMAT course. This is part 2 in a series of posts about the algorithm behind the GMAT.

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How is the GMAT actually scored? Here are some more questions that students frequently have about its algorithm.

1. My score doesn’t seem to match my performance: I only got a few questions wrong, but my score isn’t as high as I thought it would be / I got a bunch of questions wrong, yet my score seems higher than it should be.

Most exams are linear assessments, like the SAT or your 10th grade history final. These are scored by counting the number of questions you answer correctly, and sometimes by penalizing for each question you answer incorrectly. The result, a raw score, is then converted to a scaled score, like the 600-2400 range for the SAT.

A computer-adaptive test (CAT) works very differently. It doesn’t really care as much about how many you get right or wrong, but rather which questions you get right and wrong. The CAT algorithm estimates your ability based on a variety of criteria, including the difficulty of a question. After each question, it evaluates your response and updates this estimate. When the test is over, the algorithm converts your quantitative and verbal ability estimates into the quantitative and verbal scaled scores, and then separately combines your quantitative and verbal ability estimates to calculate the overall score.

2. Do the first X number of questions matter more?

Many variables that come into play when the CAT selects your next question. One of them is the CAT’s current estimate of your ability. It uses this estimate to select questions that will be most useful in refining that estimate (if you’re a high performing student, giving you low difficulty questions isn’t usually as useful in discerning your true ability as giving you harder questions, and vice versa). What is important to remember is that you should not try to guess how you are doing by whether the question in front of you seems easy or difficult; every question deserves your full attention. With that understood, unless you have completely bombed the test, it is usually the case that missing a couple of very hard questions late in the test will have a smaller effect on your final score than missing a couple of very easy questions earlier, not because of their position within the test but because of their levels of difficulty.

3. How severe is the penalty for not finishing a section?

The penalty is significant. You can expect your scaled score to decrease by roughly 1 point for every question that you don’t answer. For example, if you correctly answer every question you encounter but fail to answer the last five, you generally won’t score higher than a 46.

4. I took the GMAT and got a 710, 44q/44v/6 AWA. A friend of mine happened to take the test 6 days later and get the exact same quant/verbal scaled scores but he got a 720. How this could happen?

Both the individual section scores and the overall score are calculated using an estimate of your Math and Verbal abilities derived from your performance on the CAT. Your overall score is not calculated from your section scores. Because your underlying ability estimate might be slightly different from your friend’s, your overall scores might be different. For example, there are a range of ability estimates that translate into a Verbal score of 40, and there are a range of ability estimates that translate into a Math score of 42. Depending on which specific estimate is calculated for you, your overall score could range from 660 to 680. Please note that the Standard Error of Measurement (SEM) on the overall score for GMAT is 29 points, so scores of 660 – 680 all fall within the standard error.

Check back next week for part 3. Until then, do your homework!