SIMBAD references

We generalize the classical analytical approach by Ryle, Longair, and Banhatti, to include the unified scheme in statistical investigations of double radio source parameters. We discuss distributions of such observable parameters, on the basis of a generalized version of the classical intrinsically symmetric model. Our main goal is to see how the observations should differ according to the unified scheme for quasars and radio galaxies, by including in the model the possibility of an an isotropic viewing angle distribution. In addition, we allow for a variety of intrinsic asymmetries, emphasizing the importance of the intrinsic misalignment angle, pay attention to the lifetime bias, deforming the observed samples, and warn of the possible influence of the Doppler boosting biases. We utilize numerical calculations for more flexible and realistic models, together with the analytical approach, and construct double source tests of the unified scheme, to be applied in Paper II on extensive data.