It's not that women can never be better candidates, it is merely that this is unlikely.
Consider a set of applications, 20% of which come from women (fairly typical numbers, from what I've read). Assume women and men are equally skilled. If 30 interns are selected without bias, the odds of choosing at least 60% women (18/30) is quite small:
In [1]: from scipy.stats import binom
In [2]: rv = binom(30, 0.2)
In [3]: 1-rv.cdf(0.60*30)
Out[3]: 2.8432472531925157e-07
So unless the applicant pool was extremely unusual, it is unlikely that a pool of 2/3 women was selected due to merit.Anyone have more exact numbers to plug into this calculation? Perhaps kamens can give us some more exact numbers?
(Of course, in a much smaller applicant pool, e.g. 6 students, you might arrive at results like this due to random chance.)