  The population of radio-loud stars has to date been studied primarily through
either targeted observations of a small number of highly active stars or
widefield, single-epoch surveys that cannot easily distinguish stellar emission
from background extra-Galactic sources. As a result it has been difficult to
constrain population statistics such as the surface density and fraction of the
population producing radio emission in a particular variable or spectral class.
In this paper we present a sample of 36 radio stars detected in a circular
polarisation search of the multi-epoch Variables and Slow Transients (VAST)
pilot survey with ASKAP at 887.5~MHz. Through repeat sampling of the VAST pilot
survey footprint we find an upper limit to the duty cycle of M-dwarf radio
bursts of 8.5 per cent, and that at least $10 \pm 3$ per cent of the population
should produce radio bursts more luminous than $10^{15}$ erg s$^{-1}$
Hz$^{-1}$. We infer a lower limit on the long-term surface density of such
bursts in a shallow 1.25 mJy PSF$^{-1}$ sensitivity survey of $9^{+11}_{-7}
\times 10^{-3}$ deg$^{-2}$ and an instantaneous radio star surface density of
$1.7 \pm 0.2 \times 10^{-3}$ deg$^{-2}$ on 12 min timescales. Based on these
rates we anticipate ${\sim}200 \pm 50$ new radio star detections per year over
the full VAST survey and ${\sim}41\,000^{+10\,000}_{-9\,000}$ in
next-generation all-sky surveys with the Square Kilometre Array.
