USMLE Step 1 – 2010 Percentile Score

Hello everyone.  I received a phone call from a fellow medical student about determining a percentile score, and I told this person that it could be possible to figure out the percentile score this year from the information that the NBME gave us.

According to my score report (and others based on the information I’ve gathered), the NBME states:

“This score is determined by your overall performance on Step 1.  For recent administrations, the mean and standard deviation for first-time examinees from U.S. and Canadian medical schools are approximately 221 and 24, respectively, with most scores falling between 140 and 260.  A score of 188 is set by USMLE to pass Step 1.  The sandar error of measurement for this scale is six points.”

Making the assumption that USMLE scores follow a “normal (Gaussian) distribution” we can figure out the percentile grade.  Of course I do not know how big of an assumption I am making by saying that USMLE scores follow the normal bell curve.  Please note I am not a statistician.

So lets assume you have a three digit score of 245 on the Step 1 and would like to know percentile you fall into (I picked 245 for easy math – I was not fortunate enough to score this high).  As we know from our Step 1 studying, 68% of the population falls into the area of one standard deviation on both sides of the mean.  That means that 34% of the population falls on the upper half of this mean.  The mean on a percentile graph is of course 50%.

So we can say that if you received 24 points away from the mean in either direction (because that is one standard deviation according to the NBME) then you are 34% away from the mean in the same direction.  In this case if you scored a 245 then you are exactly 24 points above the mean.  We can also say then that you are 34% above the 50th percentile putting you into the 84th percentile.  Any score can be figured out using ratios of this.  Of course I realize my math is probably wrong, but this will give a person an estimate.

Keep in mind, my math could be TOTALLY wrong, but it seems to work out in my brain.  Here is a table with my calculated percentile scores.  Any corrections on my math would be appreciated.

Score Percentile (Estimate)
149 <1%
173 2.3%
197 16%
209 30%
221 50th Percentile 
233 70%
245 84%
269 97.7%
293 99.9%

[Similar Post – Check Out Real Board Scores for Step 1]