The null-correlation approach has been used to study the distribution of the 3CR sample of radio galaxies in the Hubble diagram, with the following results: This sample is about complete at flux density limit $S_{178} = 10$ Jy, a relatively small number of strong sources $S_{178}\gt 100$ Jy are missing (that correspond probably to local sources). The radio luminosity distribution function is given by a power law $\propto L^{\gamma(z)}$ with $\gamma(z) \approx 2$, which interprets the large scatter of the distribution in the Hubble diagram. Because of such a distribution in luminosity, this sample is not adapted for deriving the world model. The evolutionary effects are not substantial enough to be revealed within the range of observations.