Top: values of the “clustering similarity” for all tested pairs of parameters (n_s,δ), obtained from the analysis of a typical data set built from a realization of the reference model  = (n_s = 10^-5Mpc^-3,δ = 5°), indicated by the white cross. For all models considered here, a uniform distribution of the sources was assumed. Bottom: confidence contours of 68% (red), 95% (light blue) and 99% (dark blue) extracted from the same data set . These plots can be interpreted as giving the regions of the parameter space that are most compatible with the reference data set (see text for details).