Time discounting: Declining impatience and interval effect

Most studies have not distinguished delay from intervals, so that whether the declining impatience really holds has been an open question. We conducted an experiment that explicitly distinguishes them, and confirmed it at short delay such as less than 8-week delay. This implies that people make dynamically inconsistent plans. We also found the interval effect that the time discount rate decreases with prolonged intervals. We show that the interval and the magnitude effects are caused because intertemporal choice is made partially based on the differential in reward amount, while Weber’s law explains neither the delay nor the interval effects sufficiently.