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Activity Number:
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311
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Type:
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Contributed
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Date/Time:
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Tuesday, August 5, 2008 : 2:00 PM to 3:50 PM
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Sponsor:
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WNAR
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| Abstract - #302530 |
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Title:
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Using Nonlinear Mixed Models To Analyze Characteristics of Discounting Behavior
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Author(s):
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Susan K. Mikulich-Gilbertson*+ and Thomas J. Crowley and Laetitia Thompson
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Companies:
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University of Colorado Denver and University of Colorado Denver and University of Colorado Denver
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Address:
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4200 East 9th Avenue, #C268-35, Denver, CO, 80262,
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Keywords:
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nonlinear mixed models ; delay discounting ; random effects ; hyperbolic function ; substance users ; adolescents
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Abstract:
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Prior two-stage analyses suggest adults discount smaller rewards more rapidly, real and hypothetical rewards similarly, and that substance users (SU) discount delayed rewards more rapidly than nonusers. SAS NLMIXED was used to evaluate different models for comparing discounting in adolescents and to assess reward characteristics. Multiple delay intervals and reward paradigms were evaluated in 40 SUs and 40 controls. Nonlinear models of mathematical functions were compared between groups and assessed reward type and magnitude. Exponential models found that SUs discounted delayed rewards more rapidly but hyperbolic functions fit best and found no differences. Including random rate effects improved model fit but hampered convergence. Multivariate hyperbolic models found both groups discounted smaller rewards more rapidly, but only SUs discounted hypothetical and real rewards differently.
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