NATIONAL BOARD OF MEDICAL EXAMINERS®
Subject Examination Program
Comprehensive Basic Science Examination
Score Interpretation Guide
NBME® subject examinations provide medical schools with a tool for measuring examinees' understanding of the basic
sciences. Although these examinations are designed to be broadly appropriate as part of overall examinee assessment,
course objectives vary across schools, and the congruence between subject examination content and course objectives
should be considered when interpreting test scores and determining grading standards. Specifically, subject examination
scores should not be used alone, but rather in conjunction with other indicators of examinee performance in determination
of grades.
Subject Examination Scores
The subject examination score is scaled to a mean of 70 and a standard deviation of 8. A CBSE score of 70 is
approximately equivalent to a score of 200 on the United States Medical Licensing Examination® (USMLE®) Step 1. The
vast majority of scores range from 45 to 95, and although the scores have the "look and feel" of percent-correct scores,
they are not. Because the CBSE and USMLE Step 1 cover very similar content, this scale provides a useful tool for
comparing the scores of your examinees with those of a large, nationally representative group taking the licensing
examination at the end of the second year of medical school. Additional information about the relationship between CBSE
scores and USMLE Step 1 scores is provided in the table on the next page.
Unlike percent-correct scores, subject examination scores are statistically equated across test administrations. Scores
are statistically adjusted for shifts in test difficulty across different forms of the examination. This makes it possible to
track school and examinee performance over time.
Precision of Scores
Measurement error is present on all tests, and the standard error of measurement (SEM) provides an index of the
(im)precision of scores. The SEM indicates how far an examinee’s score on the examination might stray from his/her
“true” proficiency level across repeated testing using different sets of items covering the same content. Using the SEM, it
is possible to calculate a score interval that will encompass about two thirds of the observed scores for a given true score
by adding and subtracting the SEM from that score. For this examination, the SEM is approximately 3 points. For
example, if an examinee’s true proficiency on the examination is 60, the score he/she achieved on the examination will
usually (two times out of three) fall between 57 and 63 (60 - 3 and 60 + 3).
Score and Performance Feedback
Summary information on the examinee group tested, examination purpose and number of items scored is provided on
each page of the feedback. The Roster of Scaled Scores reports a total test scaled score for each examinee. Reported
scores also appear in a comma separated text file that can be downloaded and used to export scores. An Examinee
Performance Profile, which graphically displays content areas of strength and weakness, is provided for each examinee.
If there were at least 2 examinees, Scaled Score Descriptive Statistics for reported scores are provided along with a
Frequency Distribution of the total test scaled score. If there were at least 10 examinees for a single form administration,
a detailed Content Area Item Analysis Report is provided. Content area item descriptors and group item performance also
appear in a file that can be downloaded. If there were at least 10 examinees for a single form administration or 20
examinees for a multiple form administration, a Summary Content Area Item Analysis Report is provided.
If there were at least 15 examinees, a School Summary Performance Profile, which graphically displays areas of strength
and weakness in each major content area for your specific test administration, is provided.
An approximate USMLE performance equivalency table and current norms are attached. Previous norms can be found
on the NBME Services Portal (NSP).
