The effects of differing response types and price manipulations on demand measures

Animals' behavioral needs have become an important component of animal welf are legislation. Behavioral economics provides a framework for the study of such needs. A function, analogous to a demand function relating consumptio n rate to price, can be obtained by increasing the price (or work) required for access to a commodity. This experiment investigated the effects of dif ferent response types and price manipulations on these functions. Six hens pushed a door or pecked a key for food under open economic conditions (shor t experimental sessions and supplementary food). In Part 1, the number of d oor pushes required (fixed-ratio schedule) was increased each session, and the force needed to push the door was increased across conditions. In Part 2, the force needed to push the door was increased session to session, and the fixed-ratio schedule was increased across conditions. In Part 3, the nu mber of key pecks required was increased each session. Both response types produced similarly shaped (approximately linear in logarithmic coordinates and downward sloping) demand functions when price was increased by increasi ng the number of responses required. These imply an elastic demand for food under these conditions. In contrast, increasing the force required to push the door resulted in highly curvilinear functions. These functions indicat ed little change in consumption across lower door forces and abrupt drops i n consumption at higher force requirements, implying mixed elasticity in th e animals' demand for food. The differences between the shapes of the two f unctions seem to arise from the different ways that the two price manipulat ions alter the time taken to complete the work required. Increasing the fix ed-ratio requirement necessarily increases the time needed to complete each response unit, whereas increasing the force requirement does not. The diff erent shapes of the functions were robust when either force or number was v aried across sessions and the value of the other was varied over conditions . They were also robust when the price increases were taken from different conditions, showing that the shapes of the functions were independent of th e place in the experiment in which the price was examined. Unit price (whic h combines number and force into a single price measure) unified the data f rom the two price manipulations to a large degree, producing moderately cur ved functions. However, there was some variance around the unit price funct ions, and this was attributable to the different shapes of the underlying f unctions. The data suggest that different price manipulations may give diff erent measures of animal demand but that unit price might provide some unif ication.