I rather skip all technical details on ultracool dwarfs and binary stars, reviews on star formation studies, like initial mass function (IMF), astronomical survey studies, which Allen gave a fair explanation in arxiv/astro-ph:0707.2064v1 but want to emphasize that based on simple Bayes’ rule and careful set-ups for likelihoods and priors according to data (ultracool dwarfs), quite informative conclusions were drawn:

1. the peak at q~1 is significant,
2. lack of companions with a distance greater than 15-20 A.U. (a unit indicates the distance between the Sun and the Earth),
3. less binary stars with later spectral types,
4. inconsistency of undetected low mass ratio systems to the current data, and
5. 30% spectroscopic binaries are from ultracool binaries.

Before, asking for observational efforts for improvements, it is commented 75% as the the upper limit of the ultracool binary population.