Behavioral economics of human drug self-administration: progressive ratio versus random sequences of response requirements.

Progressive-ratio (PR) schedules have been used widely to examine the relationship between drug consumption and drug price (i.e. demand curves) in the study of the behavioral economics of drug abuse. Sequential effects produced by the increasing response requirements of progressive-ratio schedules might influence the shape of demand curves for drug reinforcers. This study compared progressive ratio schedule and random sequences of ratio requirements, each incremented across sessions in a within-subject design, to determine if they produced similar behavioral economic and traditional measures of reinforcer efficacy. Self-administration of standardized cigarette puffs (70 cc each) was studied with eight smokers. Puffs were available at nine ratio requirements (e.g. 3, 100, 300, 600, 1500, 3000, 6000, 12000, 24000 responses/three puffs), presented in ascending (progressive-ratio schedule) or random sequence across daily sessions. The parameter estimates obtained on measures of reinforcing efficacy (e.g. breakpoint, peak response rates, elasticity of demand) were similar for both methods of incrementing prices. We found no evidence that PR and random sequences of fixed-ratio (FR) schedules, incremented across daily sessions, resulted in different demand curves.