Clusters of galaxies. Panel a: rank-size plots of galaxy clusters measured by the number of galaxies they contain. In this case, there are strong deviations from Zipf’s law for both the catalogs we considered. Panel b: large-scale statistical fluctuations in parameter R of the two catalogs as a function of the number of groups M. Even when M is large, the parameter R is close to one. This implies that no strong fluctuations are observed. The black dotted line is the fluctuation parameter of a synthetic set of N = 10³ elements, which adhere to Zipf–Mandelbrot law with parameters γ = 0.27, Q = 5, and no statistical noise.