  Using our new Binary Population and Spectral Synthesis (BPASS) code we
explore the affect of binary populations on the integrated spectra of galaxies.
We also explore the interplay of binary populations and a varying maximum
stellar mass. We compare our synthetic populations to observations of H$\alpha$
emission from isolated clusters and H$\alpha$ and FUV observations of galaxies.
We find that observations tend to favour a pure stochastic sampling of the
initial mass function although the evidence is not significant. We also find
that binaries make a stellar population less susceptible to the stochastic
effects of filling the IMF. Therefore making it more difficult to determine if
there is a variable maximum stellar mass.
