It is not easy to compare the two, but I'm afraid your sister is wrong.

Pikeville College's DO program, for example, accepts roughly 27% of applicants. Tennessee's MD program has an acceptance rate of about 24%. While acceptance rates have their limitations, this is quite a bit higher than an acceptance rate of 10-20% that is typical of the ultra elite MBA programs.

MD/DO programs tend to have higher avg. GPA than MBA programs. However, MD/DO applicants tend to have far lower work experience than MBA applicants.

A little out of scope but what if the question were stated as--

which is more difficult to gain admissions to; a top 10 business school, top 10 medical school, or top 10 law school?

Having studied a few LSAT CRs and RCs and seen the GPAs of some of those kids that get into Yale, I'd have to say Law School isn't exactly a cakewalk.

I would say that the 3 professional schools value different elements. I would disagree with your sister's statement that it is more difficult to get into med school than into any business school, but I will agree that generally it is more difficult to get into med school. I'd counter that admission to almost any med school is professionally fine, while going to lower ranked business schools and law schools might be career suicide.

The difficulty with medical schools is that you almost have to be dedicated from day one of college - and possibly even earlier. You need to establish a foundation in biology, chemistry, etc. I did my undergrad at UCLA, and there are A LOT of aspiring doctors there that study their asses off from the moment they get to campus. You need stellar grades and a high MCAT to get into med school, and the classes that you must take are filled with highly competitive people fighting for the same grades.

Law school is also all about grades and test scores. The average GPA at the top 3 is about 3.9 - let me repeat, the AVERAGE GPA at the top 3 is about 3.9. That's higher than any medical school, but again med school applicants must take more challenging classes in general. It's certainly well higher than any business school. The average LSAT at the top schools is around the 98-99th percentile. A GMAT equivalent would be about 750-760 - imagine how competitive things would be if that was the average score at the top business schools. You must also remember that a low GPA or GMAT can be overcome for business school, but a low GPA and especially a low LSAT are killers for law school.

Admit rates for medical schools are the toughest; the majority have single digit admit rates. Take into account the ultra-high grades that people are competing with and gaining admission is a frightening prospect. Still, because the admit rates are so low, people tend to submit a lot of applications for med school, so it's hard to say how those rates compare to Law Schools (slightly better) and Business Schools (much better).

Business School has the easiest requirements in terms of grades and test scores, but it is the only one that significantly factors in work experience and activities. I would say that there are 4-6 business schools that approach the selectivity of the top law schools and med schools, but generally speaking, it's easier to get into business school. But to say that any med school is more difficult to get into than any business school is not true.