A statistical analysis of nongravitational parameters (A 2 ) looking for evidence relating to the evolution of cometary nuclei is presented. The sample is restricted to short-period comets but is otherwise essentially complete up to 1990. Alternative representations of the advance or delay of the time of perihelion passage (ΔP', ΔP″, ΔP e ) are introduced on the basis of simple theory. A correlation with the light curve perihelion asymmetry previously shown to exist for ΔP' (Festou M. C. et al., 1990, Nat, 345) is interpreted as evidence for a statistical increase of the free-sublimating fraction of the nuclear surface and/or a decrease of the nuclear radius with perihelion distance