And if we do, we can use the formulae above to generate a scale that looks like this:Īpproximate conversion between raw score and three digit score for USMLE Step 2 CK. Note that, although the distribution of Step 2 CK scores is not perfectly normally distributed, it’s probably close enough to treat it as such. The distribution of USMLE Step 2 CK scores. Lately, the mean Step 2 CK score has been 242 with a standard deviation of 17.Īnd we also know that the overall distribution of Step 2 CK scores looks like this: See, from the USMLE’s Score Interpretation Guidelines, we already know the mean and standard deviation for recent administrations of the Step 2 CK exam. Until Raymond et al laid it all out there for us. Although I was able to work out the relationship between the raw and the scaled score for early versions of the USMLE, I hadn’t stumbled on the necessary data to do this for contemporary versions of the exams. The trouble is figuring out what values to plug in for the variables in the equations. The three-digit scaled score is just a linear transformation of the z (standardized) score. The general methodĪs I’ve discussed elsewhere, the three-digit USMLE scaled score is just a T-score. This, of course, is a very interesting piece of data that we can use to approximate how many questions must be answered correctly to pass USMLE Step 2 CK. And the standard deviation was 8.3% to 8.9% across the various test forms. The authors note that on this high-stakes medical licensing test with approximately 320 questions ( read: USMLE Step 2 CK), the mean percentage of five-answer multiple choice questions answered correctly ranged from 73.4% to 74.8%. Wait a second… this is sounding kinda familiar… See, they used data from “an examination for physician licensure.”Īn examination with “approximately 320… test items.” And I guess that’s a good point, as far as it goes.īut what’s more interesting is the dataset they used to make this point. The paper is written by psychometricians with the goal of addressing something completely different: how many incorrect answer choices should be included with multiple choice questions? Their point is that, on an exam where most questions are answered correctly, an answer choice that is chosen by <5% of test-takers may still serve a useful role as a distractor. The key piece of information to help us translate percentages to USMLE three-digit scores comes from this paper:Ī paper written by NBME authors contains data that helps us convert percentages of items answered correctly to USMLE three-digit scores. After all, the USMLE does not provide precise details on how they calculate the three digit score.īut lately, I happened upon a piece of data that helps shed some light on this issue for a related exam. In discussing this, I was pretty honest that some of my calculations were based on assumptions and guesswork. I hypothesized that passing USMLE Step 1 probably required answering around 65% of questions correctly – which suggested that each correctly-answered question thereafter was worth around 1 point. Back in 2019, as part of my quest to convince whoever will listen that USMLE scores aren’t as useful for residency selection as we act like they are, I wrote about how many points each USMLE Step 1 question is worth.
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