Method Article

Measuring Delay Discounting in Humans Using an Adjusting Amount Task

DOI:

10.3791/53584

January 9th, 2016

In This Article

Summary

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Delay discounting refers to a decline in the value of a reward when it is delayed relative to when it is immediately available. We outline a computer-based delay discounting task that is easy to implement and allows for the quantification of the degree of delay discounting in human participants.

Abstract

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Delay discounting refers to a decline in the value of a reward when it is delayed relative to when it is immediately available. Delay discounting tasks are used to identify indifference points, which reflect equal preference for two dichotomous reward alternatives differing in both delay and magnitude. Indifference points are key to assessing the shape of a delay-discounting gradient because they allow us to isolate the effect of delay on value. For example, if at a 1 week delay and a maximum of $1,000, the indifference point is at $700 we know that, for that participant, a 1-week delay corresponds to a 30% reduction in value. This video outlines an adjusting amount delay-discounting task that identifies indifference points relatively quickly and is inexpensive and easy to administer. Once data have been collected, non-linear regression techniques are typically used to generate discounting curves. The steepness of the discounting curve reflects the degree of impulsive choice of a group or individual. These techniques have been used with a wide range of commodities and have identified populations that are relatively impulsive. For example, people with substance abuse problems discount delayed rewards more steeply than control participants. Although degree of discounting varies as a function of the commodity examined, discounting of one commodity correlates with discounting of other commodities, which suggests that discounting may be a persistent pattern of behavior1.

Introduction

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Delay discounting is a behavioral phenomenon that affects many situations people encounter Delay discounting refers to the fact that temporally proximal rewards are more highly valued than temporally distal rewards. That is, the value of rewards decline with delays. This is an important process because many choices that people make involve a tradeoff between immediate low quality outcomes (e.g., a piece of cheesecake after dinner) and delayed high quality outcomes (e.g., long-term health). Delay discounting has also been observed in a variety of species in addition to humans2,3, including monkeys4,5, rats6,7, and pige....

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Protocol

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The protocol was approved by the Institutional Review Board at Utah State University. The steps outlined below should serve as a guide for programming and conducting a delay discounting task.

1. Setting up a Delay Discounting Task

  1. Choose the range of delays for which discounting will be assessed.
    NOTE: For example, a typical scenario would use delays that range from 1 week to 25 years. The selected delays should follow, by convention, an approximately exponential progression (e.g., 1 week, 2 weeks, 1 month, 2 months, 6 months, 1 year, 5 years, and 25 years)
  2. Choose the maximum amount of money that will be ....

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Results

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Delay discounting results are commonly analyzed by fitting curvilinear regression models to both the median indifference points from the groups and indifference points from individual participants for each outcome. Median group indifference points are used because the indifference points for a sample are usually not normally distributed. Three non-linear regression models are commonly used: those suggested by Mazur (Equation 1)8, Myerson and Green (Equation 2)35, and.......

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Discussion

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This video describes the steps that should be taken to conduct a delay discounting experiment using the adjusting amount task. The adjusting amount task is relatively quick to conduct (10 - 15 min per participant) and produces reliable data. The adjusting nature of the task provides a fine-tuned analysis of an individual participant's degree of discounting. Since the task is computer-based data collection is automated, which limits human-error and influence during the data collection process. Typically the task is us.......

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Disclosures

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The authors have nothing to disclose.

Acknowledgements

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Preparation of this manuscript was supported in part by grant R01DA029100 from the National Institute on Drug Abuse.

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
ComputeranyMac or Windows
Programming SoftwareVisual Studioshttps://www.visualstudio.com
Data Analysis SoftwareThe R Foundationhttp://www.r-project.org
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References

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  1. Friedel, J. E., DeHart, W. B., Madden, G. J., Odum, A. L. Impulsivity and cigarette smoking: discounting of monetary and consumable outcomes in current and non-smokers. Psychopharmacology. 231 (23), 4517-4526 (2014).
  2. Bickel, W. K., Odum, A. L., Madden, G. J.

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Tags

Indifference PointNon linear RegressionDiscounting CurveImpulsive ChoiceSubstance AbuseHuman ParticipantsCommodity AssessmentExperimental Procedure

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