Histogram of the spectroscopic (z_s, red solid) and photometric (z_p, blue dashed) redshifts of the cluster member candidates (N_zs and N_zp) within 500 kpc of the example cluster, 2XMMi J143742.9+340810. The green dotted histogram represents the distribution of z_p of field galaxies within the same region. The cluster spectroscopic and photometric redshifts are represented by red solid and blue dashed vertical lines, respectively, and are listed in the upper corner.