nan, I have the NU application right in front of me, so I'll write what it says:
"Northwestern does not defer Early Decision applicants into the Regular Decision applicant pool. If you are denied admission under ED, you may not reapply under RD..."
This comes straight from this year's application that I recieved in the mail some time ago. I'm not exactly sure how much higher the test score average is for ED, but I have the viewbook somewhere and I know it is significantly higher. I'm just saying to consider all options becuase doing ED at NU could be B-A-D.