Abstract. Use of the differential distribution p(V/V_m) of the V/V_m-variable rather than just the mean leads directly to the cosmological number density without any need for assumptions about the cosmological evolution of the underlying (quasar) population. Calculation of this number density n(z) from p(V/V_m) is illustrated using the best sample that was available in 1981, when this method was developed. This sample of 76 quasars is clearly too small for any meaningful results. So the method is applied to a much larger cosmological sample of over 300 quasars to infer the cosmological number density n(z) as a function of the depth z.