We investigate the large-scale distribution of galaxy clusters taken from several X-ray catalogs .
Different statistics of clustering like the conditional correlation function ( CCF ) and the minimal spanning tree ( MST ) as well as void statistics were used .
Clusters show two distinct regimes of clustering : 1 ) on scales of superclusters ( \sim 40 h ^ { -1 } Mpc ) the CCF is represented by a power law ; 2 ) on larger scales a gradual transition to homogeneity ( \sim 100 h ^ { -1 } Mpc ) is observed .
We also present the correlation analysis of the galaxy distribution taken from DR6 SDSS main galaxy database .
In case of galaxies the limiting scales of the different clustering regimes are 1 ) 10-15 h ^ { -1 } Mpc ; 2 ) 40 - 50 h ^ { -1 } Mpc .
The differences in the characteristic scales and scaling exponents of the cluster and galaxy distribution can be naturally explained within the theory of biased structure formation .
We compared the density contrasts of inhomogeneities in the cluster and galaxy distributions in the SDSS region .
The value of the density contrast should be taken into account to reconcile the observed gradual transition to homogeneity with the apparent presence of structures on the corresponding scales .
The estimation of the relative cluster-galaxy bias ( comparing number of clusters in different SDSS regions with corresponding number of galaxies ) gives the value b = 5 \pm 2 .
The distribution of real clusters is compared to that of simulated ( model ) clusters ( the MareNostrum Universe simulations ) .
We selected a cluster sample from 500 h ^ { -1 } Mpc simulation box with WMAP3 cosmological parameters and \sigma _ { 8 } = 0.8 .
We found a general agreement between the distribution of observed and simulated clusters .
The differences are mainly due to the presences of the Shapley supercluster in the observed sample .
On the basis of SDSS galaxy sample we study properties of the power law behavior showed by the CCF on small scales .
We show that this phenomenon is quite complex , with significant scatter in scaling properties , and characterized by a non-trivial dependence on galaxy properties and environment .