Unlike many others who have mentioned, the interviewers were all very pleasant and respectful. The whole process feels like a giant aptitude test, but there were no crazy brain teasers like many suspect. Everything listed on your resume is therefore subject to scrutiny. Some questions were not formulated the best way and therefore seemed trickier than they really were. If you don't feel well enough on the day of the interview, I suggest you try to reschedule. You really need to make sure your mind is at its sharpest on the day of the interview.

How do you know if two proportions from the same population, answering the same question, are significantly different?