USMLE Scoring System

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USMLE Scores

Ok, seeing as I'm bored, and the topic of USMLE score interpretation came up in another thread recently, I thought I would clarify a few things for people who are not so certain about how the USMLE is scored. You are sitting an exam prepared and scored by the NBME.

When you receive your Score report, it will have two life-defining numbers printed on it. One is your 3-digit score. The other is your 2-digit score.

It should IMMEDIATELY be noted that NEITHER of these scores are DIRECTLY related to your performance. That is to say, they are representative of how you performed, but neither tells you how many questions you got correct.

It should also be noted immediately that the 2-digit score is NOT A PERCENTILE, nor is it a percentage. We will discuss this further later.


As the 3-digit score causes less confusion, lets deal with this first.:

-Your exam is made up of 7 blocks of 50 questions each.
-You have answered 350 questions.
-And yet the maximum theoretical 3-digit score is 300. How does this work??

Nobody except the National Board of Medical Examiners knows exactly how the 3-digit score is derived from your actual points in the exam. What we do know is that:

- Your 3-digit score IS derived from your actual performance in the exam.
- You are then looked at in comparison to other Test takers from the previous 3 months
- You are compared against the recent average for US/Canadian students.

All these factors are taken into account for your 3-digit score to be derived. This is the greyist area of the entire process, as the NBME have never actually told anyone how they derive this number.

You will note above that I referred to 300 as the THEORETICAL maximum 3-digit score. It has been personally confirmed to me by my professor who once worked for ECFMG, that it is IMPOSSIBLE to attain a score above 295 in the 3-digit score

The passing mark for USMLE Step 1 on the 3-digit scale is 182.



Now to the 2-digit score:

- The 2-digit score is a direct representation of your 3-digit score on a scale which is easier for people to understand.
- for instance, the passing mark is 182. This directly corresponds to 75 on the 2-digit scale.
- Hence, we can say, the 2-digit passing mark is 75.

Remember, this is NEITHER A PERCENTAGE NOR A PERCENTILE.

Let me quickly discredit anyone who calls the 2-digit score a percentile:
- A "percentile" tells you what percent of test takers you scored better than.
- NBME don't give us this information in our score reports. They stopped giving percentiles in May 1999.
- If 75 is the passing 2 digit score, and it was a percentile, that would mean only you and the 25 percent of people above you have passed!!! The other 75% failed????????

I DON'T THINK SO LOL

- OK, so as we said, 182 on the 3-digit scale is 75 on the 2 digit
- A range of 3-digit scores correspond to the same 2 digit score.
- e.g. 183 and 184 are both also 75. Hypothetically, let's say 186-189 is 76 etc. etc. etc.
- These ranges are variable each year.
- Generally, each year, they set 245 as 99.

99 is obviously the highest 2 digit score. Anything higher would not be 2 digits anymore!!!!
Like I said, each year, generally if you score 245 or more, you have hit 99. So 255 is 99 and 272 is 99. It doesn't matter! Anything above 245 is a 99 on the 2-digit scale.

It is a VERY clever way of scoring for reasons I will not go into, which are beyond the scope of this discussion. Essentially, the exam is created and scored in such a way so it is IMPOSSIBLE for anyone to score a maximum mark. This is very important for the NBME to maintain, once again for reasons too deep to discuss here.


OK, now let's get into the nitty-gritty statistics. This is important:

On your score report, NBME have blessed us by providing the Standard Deviation (SD) and mean 3-digit scores of recent US/Canadian exam takers.

Almost ALWAYS, it says that:

- The mean 3-digit score is 216
- The standard deviation is 24

I am now going to reveal how you calculate your PERCENTILE. As in, what percentage of people you performed better than. Many medical students are used to this form of grading, as they are often ranked in their class by a percentile. For example, if you are in the 50th percentile, 49% of people did worse than you, and 50% of people did better than you. If you are in the 100th percentile, nobody did better than you!! So by knowing your percentile, you can REALLY guage in your own eyes how well you did compared to recent US/CANADIAN graduates. This is especially useful for people who get a 2-digit score of 99.

Did you know that the lowest 99 (245) is in the 88th percentile?! That's right, 12% of people get a 99.

OK, if statistics bore you, turn away now!!


Lets take a theoretical student called Bob, who scored 242/98 on USMLE Step 1.

Let's take Bob's 3-digit score of 242 and subtract the mean:

242 - 216 = 26

Bob is 26 points above the mean.

Now divide this number by 1 Standard Deviation:

26 / 24 = 1.08

This number 1.08 is called the z-score (pronounced zee score). It tells you the number of standard deviations above or below the mean that Bob's score was. He was 1.08 SDs above the mean.

Now we have to use a z-score statistical table, which is a constant comparison table. You can use any z-score table in any statistics book. I found this one online:

http://www.epatric.com/documentation...ore_table.html

Read to where it lists the number 1.00 then read accross to where it adds 0.08 (= 1.08).

In this column it says 0.8599 which is roughly ~0.86

So now Bob knows he is in the 86th percentile. This means that in comparison to the recent test takers in US/Canada, he scored better than 85% of people, and only 14% of test takers scored better than him. Well Done Bob!!


There is much more to be said on this subject, but I hope I clarified some of the intricacies of this labyrinthine scoring process. I will, of course, happily answer anybody's questions, and take to debate with those who disagree with anything I've written.


Credit goes to the original uploader of this article, drshah, thank you