Number distribution of clones randomly generated in the Gaussian distribution whose standard deviation corresponds to the error bars of the two parameters of all comets in the K domain in Fig. 3a (a) and the histogram of the resultant Spearman’s rank correlation coefficient ρ of 1000 new samples retrieved from Monte Carlo simulations. Panel a: colours do not correspond with those in Fig. 3. Panel b: the median of the distribution function with the 68.2% interval around the median value is 0.71, and its mode is 0.76.