Measurement error is present on all tests, and the standard error of measurement (SEM)
provides an index of the imprecision of scores. Using the SEM, it is possible to calculate a score
interval that indicates how much a score might vary across repeated testing using different sets
of items covering similar content. Plus and minus one SEM represents an interval that will encompass about two thirds of the observed scores for an examinee’s given true score. Currently, the SEM is approximately 5 for Step 1 and 6 points for Steps 2CK and 3
The standard error of difference (SED) in scores is an index used to assess whether the
difference between two scores is statistically meaningful. If the scores received by two
examinees differ by two or more SEDs, it is likely that the examinees are different in their proficiency. Currently, the SED is approximately 7 points for Step 1, 9 points for Step 2CK, and 8
points for Step 3.