As for how the CAT quantifies this third factor, the calculation involves the statistical concept of standard deviation. The greater the deviation among your areas of ability, the lower your score. In other words, the GMAT rewards generalists—test takers who demonstrate a broad range of competencies—while punishing less versatile test-takers who are not as well-rounded in terms of their skill sets. I don’t want to overstate the significance of this third factor, though. The other two—number of correct responses and difficulty level—are the primary determinants of your score.

Why is the scoring system designed to account for this third factor? Because the GMAC (Graduate Management Admissions Council) recognizes that crack mathematicians or grammarians don’t necessarily make good business managers. It’s people who can put it all together—people with an overall package of quantitative, verbal, and analytical skills—who are most likely to succeed in B-school and beyond.

But I should refine this piece of advice somewhat. When it comes to resorting to guesswork, you should also consider how far along you are in the exam section. An unlucky guess early in a section is far more damaging to your score than later in the section. Why? Toward the beginning of a section, the computer-adaptive algorithm moves you up and down the ladder of difficulty rather dramatically and quickly. In as few as four questions you can move up to the highest possible level—by responding correctly to all four questions—or down to the lowest possible level—by responding incorrectly to all of them.

Once the test establishes what it thinks is the appropriate difficulty level for you, the algorithm places a heavy burden on you to prove the system wrong—that your first few incorrect—or correct—responses were flukes and you’re actually quite a bit brighter—or dimmer—than the CAT believes. If you’ve established a low ability level, and only have a few questions remaining in the section, the CAT algorithm is not going to let you take a stab at a few very difficult questions so late in the game to let you pile up some last minute points.

Think of a GMAT score like your college GPA. Low grades during your freshman year will establish a very low GPA, and you’ll be swimming upstream the next three years to redeem yourself. But low grades during the final semester of your senior year will have almost no impact on your 4-year GPA. The analogy isn’t perfect, but it’s useful nonetheless in helping you appreciate that guesswork can do far more damage to your score early in a test section.

Pretest questions will look just like scored questions, and you won’t be able to distinguish one type from the other. So there’s no sense in trying to guess which ones are unscored, and make a quick random guess on them to afford you more time on the scored questions.

However, I’d caution against taking the foregoing advice to the extreme—for two reasons. First, if you spend too much time on a few questions, you might not have adequate time for reasoned responses to all of the questions in the section. So it’s a balancing act in terms of proper pacing. Secondly, intuition plays a role in multiple-choice testing, and second-guessing yourself can be counterproductive, because changing your initial response to a question more often than not results in an incorrect response.

To the extent that the CAT creates a broader distribution of scores, it is a better means of comparing the cognitive abilities of test-takers. This is a statistics concept that’s really pretty easy to understand on a non-technical level. Scores for multiple test-takers that all cluster closely together are less reliable for the purpose of comparing ability levels than more widely distributed scores are.

In an ideal world, perhaps a more extensive battery of tests spread over several weeks—or even months—and that includes an oral component as well would be fairer. But it comes down to a tradeoff between fairness and administrative efficiency. The testing service couldn’t provide such a test on an affordable basis, especially considering that more the a quarter-million GMAT tests are administered every year!

I don’t mean to suggest here that taking paper-based practice tests is not worthwhile. As long as they accurately reflect the style and difficulty level of the actual GMAT, they’re quite useful for additional practice. By the same token, you shouldn’t assume that any GMAT software product will be a reliable predictor of your performance on the actual GMAT. I’m not at liberty to make any specific product recommendations here, but keep in mind that some GMAT software products are better than others—both in terms of replicating the style and difficulty level of actual GMAT questions and in terms of forecasting your scores on the actual GMAT. So choose your test-prep software carefully.