How the GMAT Computer Adaptive Testing Algorithm Works

A standardized test is a regular kind of test that you must have come across before. In this kind of test, you see all the questions as soon as you open the test booklet. However, unlike the standardized, the GMAT computer adaptive testing algorithm otherwise known as a CAT displays one question at a time in CATs. It sounds a little different from what you know, right? That said, let’s see how computer adaptive testing works.

What is a Computer Adaptive Test?

A computer adaptive test (CAT) is a computer-based test that adapts to one’s level of ability. The computer evaluates the test taker’s responses and selects subsequent questions based on how well they answered each question. If you were taking the exam, the computer learns about you or your ability from previous questions, then delivers the next based on what it knows about you. For example, if you get a question that is moderately difficult and you answer it correctly you will get one that’s slightly more difficult next. However, if you answer it incorrectly, the next question presented to you will be simpler. The exam’s difficulty adapts to your level of ability.

The GMAT works on that same principle. The GMAT algorithm continuously adapts to your level of ability during the test. It then delivers the next question based on how accurately you answered the previous question.

GMAT Computer Adaptive Testing is A Test of Ability

In a standardized/linear kind of test, all candidates get the same set of questions. Unlike CAT, the score depends on the number of questions one gets right. For example, students A and B, take a 50-question test, and each gets 30 and 34 questions correct, respectively. Their percentage scores would be 60% and the second 68% respectively. This is a test of accuracy, student 1 is 60% accurate, and student 2 is 68% accurate. 

If a group of students took the same test as student 1 and 50% of the students got 30 or more questions correct, then student 1 is at the 50th percentile ability. But if only 10 % of the students got 30 or more questions correct then student 1’s ability is 90th percentile. The GMAT measures your comparative performance in relation to other test takers.

How does the GMAT computer adaptive testing algorithm measure ability?

Consider the following scenario, students A and B scored as follows in the verbal section of a GMAT exam.

Student A

$$\small{\begin{array}{l|l|l|l} 1-10 &11 – 20&21 – 30&31 – 41\\\hline 1&11&21&31\\\hline2 &12&22&32\\\hline3&13&23&33\\ \hline4&14&24&34\\\hline5&15&25&35\\\hline6&16&26&36\\\hline7&17&27 &37 \\\hline8&18&28&38\\\hline9&19&29&39\\ \hline10&20&30&40\\ \hline&&&41\\\hline V42&&&\\\hline\end{array}}$$

Student B

$$\small{\begin{array}{l|l|l|l} 1-10 &11 – 20&21 – 30&31 – 41\\\hline 1&11&21&31\\\hline2 &12&22&32\\\hline3&13&23&33\\ \hline4&14&24&34\\\hline5&15&25&35\\\hline6&16&26&36\\\hline7&17&27 &37 \\\hline8&18&28&38\\\hline9&19&29&39\\ \hline10&20&30&40\\ \hline&&&41\\\hline V33&&&\\\hline\end{array}}$$

Note: the red boxes indicate the questions the student answered incorrectly. 

Students A and B both answered 10 out of 40 questions incorrectly, they both have a 76% accuracy. But how do their abilities compare?

Understanding the CAT algorithm in this case

Student A scored a V42 which corresponds to the 96 percentile. On the other hand, student B scored V33 which corresponds to the 69 percentile. Both students had similar accuracies of 76%. However, student A showed a much higher ability if we look at their respective GMAT scores and percentiles.  

During an exam, the system randomly selects a question of medium difficulty from a pool of questions. Student A answers the first set of 10 questions correctly. The computer estimates the student’s score based on the number of questions answered correctly and their level of difficulty. Correct responses to relatively harder questions will lead to a higher score. The computer will then evaluate all eligible questions to determine the best question or set of questions to administer next. Since student A answered all the first questions correctly, the next set of questions will be relatively harder. This process continues until the system administers the number of questions required.

On the other hand, student B answered two questions incorrectly in the first set of 10. Similarly, the computer estimates this score based on the number of questions they answered correctly and their level of difficulty. The computer will evaluate all the questions available and select the next best question or set of questions. Since student B answers more questions incorrectly in the first set, the next set of questions will be relatively easier. This process continues until the system administers the number of questions required.

Question difficulty levels for students A and B

The difference in scores in the first set of questions impacted the difficulty level of the questions each student received afterward. Student A was served harder questions which were obviously of higher value than student B. Correct responses to relatively easier questions will lead to a lower score than correct responses to relatively harder questions. 

In general, the GMAT starts with a set of questions of medium difficulty. The algorithm selects them randomly since the test does not have an estimate of your ability. Your responses to these questions are compared to the historical responses of other candidates. This enables the computer to either increase or decrease the level of difficulty of the next set of questions.

The computer then assesses your responses to the second set of questions and arrives at another estimate. It uses this estimate to adjust the difficulty level of the third set of questions. This process continues until the system administers the number of questions required.

How will the adaptive GMAT computer adaptive testing algorithm affect your score?

Let’s take a look at table 1 above. By the end of the second set of questions, A has answered 2 out of 20 questions incorrectly. This represents a 90% accuracy. The computer will therefore be able to increase the difficulty level of the next set of questions. Overall A answered a total of 10 questions incorrectly and only managed a 75% accuracy level. However, the student scored a V42 which corresponds to a 96 percentile ability. This implies that by the end of the second section, A has basically proved his ability in the verbal section. Therefore, incorrect answers in subsequent sections will not adversely affect their score.

This begs the question, “Is the first set of questions more important than the rest?” The answer is yes. One incorrect answer will make you lose up to 7 points.

Are the questions that come later in the section less important? You could say yes, yet these latter sections are the ones that will ultimately set apart the very good students and those with outstanding abilities. So all questions are important, but your personal goals as you prepare to take the GMAT are even more important.

Implications as you prepare to take your GMAT

1. Build your ability

The GMAT is a test of ability, therefore during your preparation, focus on building your ability. Focus on understanding the different kinds of questions tested on the GMAT and learn the processes of solving them. Do not time yourself during the initial stages of your preparation. Instead, make sure you master the topics to a degree of 80% or higher ability. This should give you the ability to answer the tougher questions, especially in the first half of the test. 

2. Practice and measure your ability regularly

Do as much practice as you can. However, take your time to assess if and how much your ability is improving on a regular basis. Use specially designed questions to evaluate how much you have improved your weak area, or use mock tests.

3. Learn to pace yourself right

You get about 2 minutes for every question in GMAT. However, distributing your time regularly throughout the test will do you no good. Since the first 10-15 questions are relatively more important, don’t focus on timing yourself or cutting corners to save time for later. Instead, focus on answering all questions correctly. Naturally, it should take you less time to solve easier questions than the harder ones. If you’re unable to answer the initial questions on time, focus on solving the cause before taking the test.

4. Have a proper study plan

Students may be often tempted to skip certain topics that they think are less important. It’s not advisable to do that. Many topics are interlinked. As such it is impossible to tell which questions from which topics will be administered at which level. Follow a proper study plan that ensures you achieve the desired level of ability and preparedness in all topics.

Now you know what the GMAT computer adaptive algorithm is all about. Therefore, you’re ready to get started with your tests. Register with AnalystPrep anytime and get a GMAT package to start your preparation early enough.