When the participant chose one of the options, the immediate value was adjusted in the next trial up or down by half. If the participant chose the immediate reward, its value dropped by half for the next question. If he chose the future reward, its value increased by 50 percent, but delivery was further in the future. Participants made a choice between immediate and delayed rewards for each of seven delay periods one day, one week, one month, six months, one year, five years, and 25 years.
Findings for money now versus money later and cocaine now versus cocaine later replicated previous studies with single commodities. The mixed commodity conditions are novel to this study. In the money now-cocaine later choices, "participants soon became indifferent to future cocaine amounts, preferring immediate money even when the value of the future cocaine was significantly greater. That is, cocaine is discounted more steeply than money," said Bickel.
However, when the immediate reward was the drug and the future reward was money, the decline was less steep. "It took longer for the future money to lose favor compared to a lesser value of cocaine," said Bickel. Discounting rates for cocaine now versus money later were not much different than the single commodity results.
Reflecting on the implications for drug treatment programs, Bickel pointed out, "We showed that a delayed drug is discounted more than when the drug is immediately available, no matter what the other option is. In other words, drug users are less likely to use drugs wh
|Contact: Susan Trulove|