Implicitly, σ σ ( R ) and δ δ M depend on redshift, so the above probability does as well. The variance given in the 1974 paper is σ σ ( M ) 2 = Σ Σ 2 M 2 = V ⋅ ⋅ σ σ 2 M 2 = σ σ 2 M ⋅ ⋅ ρ ρ where Σ Σ is the mass standard deviation in the volume of the fluctuation.