More Brown Dwarfs in the Sun's Neighbourhood
There are 136 stars and 26 brown dwarfs known within ~20 light years of the Sun, giving a star to brown dwarf ratio of 5.2. The 26 brown dwarfs are divided into spectral classes (1 M-dwarf, 2 L-dwarfs, 18 T-dwarfs, and 5 Y-dwarfs). It appears that the brown dwarfs within ~20 light years of the Sun are not uniformly distributed. There are 21 brown dwarfs behind the Sun, but only 5 brown dwarfs ahead of the Sun in the direction of rotation of the galaxy. This non-uniform distribution of brown dwarfs is most likely due to an observation bias because brown dwarfs should be uniformly distributed like stars. What this means is that the brown dwarf census in the Sun's neighbourhood is incomplete. Assuming there are 5 more brown dwarfs in front of the Sun, the star to brown dwarf ratio decreases to 4.4. This brings it closer to the estimated star to brown dwarf ratio of ~3.3 for the Orion Nebula cluster, a star forming region.
Bihain & Scholz (2016), "A non-uniform distribution of the nearest brown dwarfs", arXiv:1603.00714 [astro-ph.SR]