Quiz: You are hiring for a position that you desperately need stability in. Your hope is that you can get someone who will still be with your company in five years. You have two qualified candidates whom you feel would be a good fit for the job and your organization. Which one should you offer the job to?

A. Woman with 10 years of experience and an MBA from a top 10 school

B. Woman with 10 years of experience and an MBA from a 2nd tier school.

Up until yesterday, I probably would have said that you should go with candidate A. MBAs from top 10 schools are hard to come by and clearly anyone who has one is smart and capable and can hold her own. But, new research by Vanderbilt Professor of Law and Economics and of Management Joni Hersch, says that the people who work the least hours are women with degrees from elite institutions.

And the women likely to work the least? Women with MBAs from select universities. Professor Hersch said: "Married MBA mothers with a bachelor's degree from the most selective schools are 30 percentage points less likely to be employed full time than are graduates of less selective schools."

That is a huge gap, which remains even after all other variables, such as years in career, number of children and spouse's characteristics are taken into consideration. (The gap is lessened by these factors, but not eradicated.)

So, if you want someone for the long term, it may be best to go with the woman from a 2nd tier university rather than the big name school.

Why is this? Some would theorize that women are pushed out, but that wouldn't explain the difference between women from different tier schools. You'd think those who survived the competition to get into a top 10 program, and then survived the program herself would have the ability to stand up for herself and not be pushed out.

It's not just women with MBAs that show this difference--the difference exists at the Bachelor's degree level as well, just not as pronounced as at the MBA level.

There are substantive differences between people who attend selective schools and those who don't--one of which is parental income. Those who attend the more selective schools tend to need fewer student loans in order to get through school. Therefore, a good question to ask, if student loans were eliminated, would some of these working women from less elite institutions opt out of the work force as well?

Now, before you immediately reject all women from top schools, understand that the majority are still in the workforce. And averages are very different from individuals. As always, make your hiring decisions based on the individuals sitting in front of you rather than consulting the averages.