Cumulative distribution of the number of BAT excesses not associated with strategy A having at least one of the strategy B list sources (see Sect. 4) within a given distance (red stepped line). The green continuous line represents the number of spurious associations evaluated using Eq. (1), while the black dashed line is the mean number of spurious associations evaluated by using a control sample of sky positions generated by scrambling the coordinates of the BAT excesses. The blue stepped line represents the true associations obtained as the difference between the red stepped line and the green continuous line. The vertical dotted line marks the radius (6.8 arcmin) that produces 5% of spurious associations.