Mass distribution function of the YAR (in black solid) and the thick disc (in dark grey dashed, and light grey dash-dotted) samples. f = N_i/N_tot represents the fractional number density where N_i is the number of stars in each bin of mass and N_tot is the total number of stars of the sample. The light grey dash-dotted histogram restricts the thick disc sample to stars with mass errors less than 0.05 M_⊙.