Me thinks I understand the NBME scoring: just a theory

[rachmoninov3]

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so here's the great big theory:

I was doing 7 blocks of random uworld questions, and realized that the sum of all my scores was a 490, which of course, looks like the score report for the NBME exams, and was in the ball park of what my scores have been. So here's the theory (and it's just a theory, but the number looked so perfect and fit percentiles, and as any math geek will tell you if it's pretty it has to be right...)

add up your score from each of the four sections.
divide that by 4
multiply that number by 7
round up or down to nearest 10.
= NBME score

 

[Pollux]

I've got a table with NBME scores and the corresponding % of questions answered correctly.

According to this table,
500 (218/90) requires 77.3% of questions to be answered correctly.
600 (240/99) requires 85.9% of questions to be answered correctly.
700 (256/99) requires 92.4% of questions to be answered correctly.

Don't know how accurate it is.
The USMLE 3-digit-score to 2-digit-score conversion is very accurate though.

 

[pseudoknot]

It's a standard score. 500 is the mean, and 100 points is one standard deviation. If you look at the table Pollux posted you see that 600 is one standard deviation above the mean (i.e., the 84th percentile) and 700 is two SDs above (97th %ile). So it's not linearly related to your percentage correct because it depends on the difficulty of each test.

 

[Pollux]

It's a standard score. 500 is the mean, and 100 points is one standard deviation. If you look at the table Pollux posted you see that 600 is one standard deviation above the mean (i.e., the 84th percentile) and 700 is two SDs above (97th %ile). So it's not linearly related to your percentage correct because it depends on the difficulty of each test.

I guess it also implies that the 3-digit-score is not in (perfectly) normal distribution, as 218 is the mean, 240 is 1 SD above, 256 is 2 SD above, and 265 is 3 SD above. The difference gets progressively smaller.

Also note that this table was probably produced back in the days where the mean was still 218. The mean 3-digit-score for the 2008 administration was 222.

 

[Saladin MD]

Also note that this table was probably produced back in the days where the mean was still 218. The mean 3-digit-score for the 2008 administration was 222.

Well, the only reason that the mean shifted was because of your score, Mr. Pollux.

 

[pohma]

I've got a table with NBME scores and the corresponding % of questions answered correctly.

where is that table from? NBME?