Distribution of the goodness of fit z_1s of sources in the GBTDS contiguous field with F146_Vega < 23.5 mag. The distribution of z_1s for luminous single sources is shown in solid black; their z_1s distribution follows a standard normal distribution. The distributions of z_1s for luminous binary sources (star + star, WD, NS, or BH) are shown in the dotted blue, dotted–dashed orange, dashed green, and solid red lines, respectively. BH+star binaries have a significant tail beyond z_1s ≳ 3, due to model mismatch.