Some characterizations of (strongly) subadditive discounting functions

The aim of this paper is to characterize some parameters which measure the “force of discount” in a discounting function (the instantaneous discount rate and the geometric mean of a discounting function), and relate them with the strong subadditivity and the so-called subadditivity of second order. We distinguish two intertemporal choice frameworks, depending on the consideration of time as an interval or both as an interval and a delay, and we establish some necessary and sufficient conditions to identify strongly subadditive and subadditive of second order discounting functions.