  We present a model to estimate the average primary masses, companion mass
ranges, the inclination limit for recognizing a rotational variable, and the
primary mass spreads for populations of binary stars. The model fits a
population's binary mass function distribution and allows for a probability
that some mass functions are incorrectly estimated. Using tests with synthetic
data, we assess the model's sensitivity to each parameter, finding that we are
most sensitive to the average primary mass and the minimum companion mass, with
less sensitivity to the inclination limit and little to no sensitivity to the
primary mass spread. We apply the model to five populations of binary spotted
rotational variables identified in ASAS-SN, computing their binary mass
functions using RV data from APOGEE. Their average primary mass estimates are
consistent with our expectations based on their CMD locations ($\sim0.75
M_{\odot}$ for lower main sequence primaries and $\sim 0.9$--$1.2 M_{\odot}$
for RS CVn and sub-subgiants). Their companion mass range estimates allow
companion masses down to $M_2/M_1\simeq0.1$, although the main sequence
population may have a higher minimum mass fraction ($\sim0.4$). We see weak
evidence of an inclination limit $\gtrsim50^{\circ}$ for the main sequence and
sub-subgiant groups and no evidence of an inclination limit in the other
groups. No groups show strong evidence for a preferred primary mass spread. We
conclude by demonstrating that the approach will provide significantly better
estimates of the primary mass and the minimum mass ratio and reasonable
sensitivity to the inclination limit with 10 times as many systems.
