One of the most common questions I get as a USMLE tutor is:
"What is the difference between the NBME Comprehensive Basic Science Self Assessments (often referred to as just NBMEs) and the UWorld Self Assessments (UWSAs)?"
For starters, the NBME and UWSA are both practice tests that students take to help them prepare for the USMLE Step 1 exam, to gauge their study progress, and to predict their final score.
There are six NBMEs that are available for purchase for $60 each (and in 2020 an additional five that are available for free). There are two UWSAs that are included in your UWorld subscription if you buy at least a 180 day subscription.
NBMEs consist of four sections of 50 questions while the UWSAs contain four sections of 40 questions. The actual USMLE Step 1 exam is made up of 7 blocks of a maximum of 40 questions per block.