Distribution of sources in the z_P1 − y_P1 vs i_P1 − z_P1 diagram of the test samples of HzQs (left), brown dwarfs (middle), and galaxies (right). Sources not selected with any method are marked in grey. Sources selected with i − z > 2 colour cut (dashed line) but rejected by the probability selection are marked as a diamond shape with a black edge. Notably, the z − y < 0.5 colour cut (dotted line) rejects all brown dwarfs from the test sample, but also a large portion of the simulated quasar sample.