Cumulative number of positive (red histogram) and negative (blue histogram) detections as a function of the σ_p (at a fixed σ_f, left panel) and σ_f (at a fixed σ_p, right panel) in units of σ. Solid black line represents the purity criterion p_c define by Eq. (1), green dashed-line represents the percentage of positive detection with HST-WFC3 counterpart p_HST and magenta dashed-line represents the percentage of positive detection with ZFOURGE counterpart p_ZFOURGE. Gray dashed-lines show the thresholds σ_p = 4.8σ and σ_f = 2.7σ and the 80% purity limit.