Sumpter, C. E., Temple, W., & Foster, T. M. (1999).
The effects of differing response types and price manipulations on demand measures.
Journal of the Experimental Analysis of Behavior,
71, 329-354.
Animals' behavioral needs have become an important component of
animal welfare legislation. Behavioral economics provides a
framework for the study of such needs. A function, analogous to a
demand function relating consumption rate to price, can be
obtained by increasing the price (or work) required for access to
a commodity. This experiment investigated the effects of
different response types and price manipulations on these
functions. Six hens pushed a door or pecked a key for food under
open economic conditions (short experimental sessions and
supplementary food). In Part 1, the number of door 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 number 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 increasing 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 indicated little change in
consumption across lower door forces and abrupt drops in
consumption at higher force requirements, implying mixed
elasticity in the animals' demand for food. The differences
between the shapes of the two functions seem to arise from the
different ways that the two price manipulations alter the time
taken to complete the work required. Increasing the fixed-ratio
requirement necessarily increases the time needed to complete
each response unit, whereas increasing the force requirement does
not. The different shapes of the functions were robust when
either force or number was varied 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 the
place in the experiment in which the price was examined. Unit
price (which combines number and force into a single price
measure) unified the data from the two price manipulations to a
large degree, producing moderately curved functions. However,
there was some variance around the unit price functions, and this
was attributable to the different shapes of the underlying
functions. The data suggest that different price manipulations
may give different measures of animal demand but that unit price
might provide some unification.
Key words: fixed-ratio schedules, demand functions, unit price,
response type, key peck, door push, hens