Brown dwarfs not as common as previously thought?

Well, this (and this and this and this) is a disappointment. It has been determined that 33 of the brown dwarfs WISE has discovered are nearby, within 26 light years, but they have turned out to be much less frequent than previously predicted, with only one of them per six stars or so. This would almost remove the possibility of one nearer than Alpha Centauri. There is still a faint hope for one at this distance:

Kirkpatrick emphasized that the results are still preliminary: it is highly likely that WISE will discover additional Y dwarfs, but not in vast numbers, and probably not closer than the closest known star, Proxima Centauri. Those discoveries could bring the ratio of brown dwarfs to stars up a bit, to about 1:5 or 1:4, but not to the 1:1 level previously anticipated.