Comparing Force and Ratio Progressions from the Behavioral Economic Unit Price Equation

Abstract

In behavioral economic demand, the currently predominant conceptualization of unit price suggests that increasing lever weight or ratio requirement should result in equal changes in unit price and thus identical changes in consumption. Data from the few studies that have compared consumption under ratio progressions and force progressions tend to show differences in consumption across the two manipulations, even with unit price adjustments. These studies, however, failed to measure the broader operant class (i.e., subcriterion responses) and the force of individual responses, so the present experiments extend this work by using a force transducer to measure responding. In Experiment 1, six rats responded for sweetened condensed milk across ascending prices composed of ratio or force progressions equated based on unit price. Consistent with prior research, results showed consumption differed across progression types, with force progressions producing more inelastic consumption across low unit prices than ratio progressions. As force criterion increased, the proportion of subcriterion relative to total responses increased. Experiment 2 aimed to investigate how these subcriterion responses impacted the demand functions obtained from the force progressions. In Experiment 2, demand curves were obtained by yoking reinforcer-by-reinforcer to the total number of responses (i.e., subcriterion and criterion) per reinforcer delivery from the force progressions for each rat. Some similar patterns of consumption were observed across the force and yoked progressions, but deviations were noted. Convergence in consumption was assessed across several candidate alternatives to unit price, with the greatest convergence produced by measures of cumulative time integral of force per 0.05-ml unit of reinforcer and mean cumulative response duration per 0.05-ml unit of reinforcer.