Using gammapy.stats to compute statistical quantities such as excess, significance and asymmetric errors from counts based data. The data array such as counts, counts_off and the background efficiency ratio alpha are passed on initialization of the WStatCountsStatistic class. The derived quantities are then computed dynamically from the corresponding class attributes such as stat.n_sig for the excess and stat.sqrt_ts for the significance. The output of the code example is shown in Fig. A.4.