Membership probability p distribution for the 498 stars selected in the direction of NGC 6618 with parallax < 1.0 mas. The field stars have p < 0.96, shown in red, while member stars have p ≥ 0.96, shown in blue. The dashed black line (N = 5) shows the threshold used for the membership p cut-off between field and member stars. The first and second bin from the left contain 250 and 36 stars, respectively, and are cut off for better visualisation of the other bins.