EFFECTS OF INCOME ON DRUG CHOICE IN HUMANS

The effects of income (money available to spend during the experimenta l session) on human choice were examined in a concurrent-schedule arra ngement. Subjects were 7 nicotine-dependent smokers, and reinforcers w ere puffs on the subject's usual brand of cigarette (''own'') and puff s on a less preferred brand of cigarette with equal nicotine content ( ''other''). Across sessions, income varied and the price of the two re inforcers was held constant, with the other puffs one fifth the price of the own puffs. As income increased, consumption of own puffs increa sed while consumption of the less expensive other puffs decreased. The se effects of income on choice were highly consistent across subjects. For some subjects, however, income had little effect on total puff co nsumption. Finally, an additional condition examined whether price and income manipulations would have functionally equivalent effects on ch oice by repeating an income condition in which the price of the other brand was increased. Although the increased price of the other puffs d ecreased their consumption in 4 subjects, 2 subjects showed increased consumption of the other puffs at the higher price. The results, when defined in economic terms, indicate that the own puffs were a normal g ood (consumption and income are directly related), the other puffs wer e an inferior good (consumption and income are inversely related), and the direct relationship between consumption of the other puffs and th eir price is defined as a Giffen-good effect. The latter result also s uggests that for these 2 subjects, price and income manipulations had equivalent effects on choice. These results extend findings from previ ous studies that have examined the effects of income on choice respond ing to human subjects and drug reinforcers, and provide a framework fo r further experimental tests of the effects of income on human choice behavior. Methodological and theoretical implications for the study of choice and for behavioral pharmacology are discussed.