Ratio between the measured and input velocity dispersion resulting from fits of artificial datasets with varying input velocity dispersions. These datasets were fitted assuming the binary properties of solar-type field star, but were created using different binary period and mass ratio distributions. For the blue “+”-signs the binary population used to create the velocity distribution follows the same field solar-type binary properties used to fit the distribution, except that the mass ratio distribution is flat rather than falling (see Sect. 4.2.1). For the green dots the massive stars follow the solar-type binary properties, while the binary properties of the low mass stars are set by the most likely binary fraction, period distribution, and mass ratio distribution observed for very low mass binaries from Burgasser et al. (2007, see Sect. 4.2.2).