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How to Use the NBME Self-Assessments to Prepare for Step 1

Despite their nondescript name, the Comprehensive Basic Science Self-Assessments (CBSSAs) offered by the National Board of Medical Examiners’ (NBME) cover material most closely related to the USMLE Step 1 exam. Consequently, they represent one of the most important resources to use to prepare for Step 1, yet many students aren't sure how to best utilize these practice tests, often referred to as "NBMEs".

Below is a comprehensive guide on how get the most out of these crucial practice tests in order to help you survive (and ace!) Step 1.

The Basics


As of today, there are 6 practice exams available under the Comprehensive Basic Science Self-Assessment (CBSSA) tab on the NBME website. Each exam costs $60 and can be purchased through the official website. Available forms include 13, 15, 16, 17, 18 and 19, with the missing numbers corresponding to “retired” exams. Older exams are no longer available through the NBME. but can be found online through unofficial websites. Don't feel compelled to seek out these retired exams; most students (including those who do excel on Step 1) don't use these old exams.


The format of these practice exams differs from the actual Step 1 exam in two key ways. First. NBME practice exams are comprised of 4 sections composed of 50 questions each. With 1 minute and 30 seconds theoretically allotted to each question, you have 1 hour and 15 minutes to complete each section and 5 hours total for the whole exam. The actual Step 1 exam is comprised of 7 sections of 40 question blocks, corresponding to 1 hour per section (7 hours total). Second, the user interface of the NBME practice exams is different from that of the actual exam, despite originating from the “official” organization, the NBME. Surprisingly, the UWorld question banks and practice exams best recapitulate the actual testing interface.

Taking the Self-Assessment


The exact timing of the first practice exam can be a contentious issue. Some argue that it should be taken at the very beginning, right before your dedicated study time. On the one hand, doing very poorly (or even failing) such an early exam can provide for a very motivated beginning to your studying. Additionally, it could give you a sense of which areas you are weak on. On the other hand, some argue that it is a “waste” of one of six crucial study aides, but this only holds true if the exam is not properly reviewed afterwards. Personally, I did not take an exam at the very beginning of my dedicated study period, ascribing to the latter rationale. Instead I took the first practice exam right after my first pass of First Aid.

Regardless, an exam (first or second) should definitely be taken several (usually at least six) weeks before your test day. Establishing a baseline score is crucial. It will lead to a drastic shift in your study approach (if you score below a 200 on your first practice test in particular, this can suggest that you will need a more intense dedicated study period to catch up).

For the remaining exams, allow for at least one to two days between them to adequately review the answers. It should be noted that some test takers combine one NBME practice exam (5 hours) with 2 of the 4 sections of a UWORLD self-assessment (2 hours) to approximate the length of the actual exam. Also, some argue that one exam should definitely be taken within the week preceding Step 1. Personally, I dedicated that week to reviewing previous questions and concepts, while taking my last practice exam 10 days before Step 1. Following this latter plan could minimize the stress of encountering new and challenging questions just days before the actual exam, however many students do feel comfortable taking a test (or two) the week before the exam, and end up doing well with this strategy.

Day Of

You should plan to take each practice exam as if you were taking the actual exam. That means you should start the same time you will begin the Step 1 exam (usually around 8.30 am). Plan to take each practice exam in one sitting, with brief breaks (e.g. 10-15 minutes) between sections and in a space with minimal distractions. The reason for these specifications is to accustom yourself with the test-taking experience. You will find that optimal performance in these exams is not only dependent on your knowledge base to date, but also your in-test concentration level. Hence, emotionally convincing yourself of the utility of each of these exams is equally important to controlling environmental factors.

Why You Don't Need to Screenshot Anymore

while you take the exam. Unfortunately, unlike question banks like UWorld, once you complete an NBME, you will no longer have access to the questions you got right, and no explanations will be provided for any questoin. One way to circumvent this issue is to take screen shots (save selected area to a file) of each question Both Mac and PC computers are able to do this, and the NBME program will not quit like UWorld if you do this (just be sure not to distribute the screen shots to others, as this is considered copyright infringement).

The Aftermath

Exam Review

If you take screenshots while you take each NBME, any and all questions can be reviewed on your own or with one of our tutors or through (often unreliable) sources online. Reviewing both your mistakes and the correctly answered questions is of pivotal importance and essentially the crux of why you should take these exams. You might be tempted to limit the time you take to review the questions, especially after such a long exam. Do not give in to this temptation. Instead take one to two days to meaningfully review all questions and simultaneously memorize the corresponding concepts.

The Score

At the end of each exam, you will also get a raw CBSSA score and a raw to three-digit score conversion table. The conversion table is unique to each exam and can change through the years even for the same exam, as NBME adds more test-takers to its statistical analyses. Hence, beware of old, third-party NBME conversion tables if you elect not to purchasing the exams and obtain them illicitly online (for several reasons, I wouldn't recommend this). Arguably one would think that the three-digit score is one of the most important aspects of the practice exam. This thought process rests on the assumption that these scores are firstly representative of one’s fund of knowledge and secondly predictive of one’s performance on the actual exam.

In both cases, this is only partly true. On the one hand, scoring below a 230 is indicative of a need to study more. On the other hand, scoring above a 240 is indicative of a good knowledge base. Except for the rare case of scores clustered in the extremes (consistently above 250 or below 210), no scoring pattern on NBMEs appears to accurately predict your performance on the actual exam (the UWorld Self Assessments tend to over-predict your test-day score, but are relatively reliable for this purpose, in contrast). It is important to understand and believe this fact early in your preparation. This will save you time from using “score calculators” searching through unreliable forums and listening to fellow classmates claiming arbitrary score correlations (“you will score within 5 points of your average”). Avoiding all this will spare you unnecessary stress and help you focus on what matters: reviewing all questions in depth and learning as much as you can in the process.

Constantine Tarabanis is an MS4 at Harvard Medical School. He tutors for the USMLE Step 1 and shelf exams with USMLE Pro.

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