that's a good question!! this has come up before, though i don't know if it was on here. it may have been on ec's peer network, or one of the yahoo groups.
i do know that all the tests are divided into percentages of content. like i remember NC3 was mainly OB (50% or something high, maybe higher than 50% its been a while!!) and then had a few other small sections of 15% and such. I know several students were upset that they got maybe 10/15 questions wrong on the small section, and did poorly in another small section, but did very well on the OB part and still failed.
The only good thing about the EC exams is getting the instant grade on the screen like computer CLEP exams. Though its hard sometimes to press submit...
sorry i couldn't help, but i know someone who knows will be along soon. there's quite a few EC people on this board!!!
I bet you Eric knows. he's a mod for this forum, and he just graduated a while ago and works in NICU....oh Eric!!! Where are you??? You took statistics!!! How do they grade the EC exams?