Mass ratio vs separation for binaries in ONC (this study), in Tau-Aur (WG01, HK03), and in Oph (P03) with T Tauri types (CTTS and WTTS) based on K − L color excess. For ONC systems, open symbols are systems taken from D12 with T Tauri types defined from a conjunction of r_K, H − K color excess, and Brγ emission. Mass ratios derived from S00 tracks are plotted.