title: Mixture models of delay discounting and smoking behavior.
abstract: Smokers exhibit an unusually high willingness to forgo a delayed reward of greater magnitude to receive a smaller, more immediate reward. The functional form of such "delay discounting" behavior is central to the discounting-based operationalization of impulsivity, and has implications for theories regarding the basis of steep discounting among smokers and treatment approaches to addiction.
  
  
  
  We examined the discounting behavior of current smokers, ex-smokers, and never-smokers to determine whether the functional form of discounting differs between these groups.
  
  
  
  Participants completed a 27-item delay discounting questionnaire (25). We used finite mixture modeling in analyzing data as the product of two simultaneous data-generating processes (DGPs), a hyperbolic function and an exponential function, and compared results to a quasi-hyperbolic (QH) approximation, in a relatively large sample (n = 1205).
  
  
  
  Consistent with prior reports, current smokers exhibited steeper discounting relative to never-smokers across exponential, hyperbolic, and QH models. A mixture model provided significant support for exponential and hyperbolic discounting in the data, and both accounted for roughly 50% of the participants' choices. This mixture model showed a statistically significantly better fit to the data than the exponential, hyperbolic, or QH functions alone. Contrary to the prevailing view, current smokers were not more likely to discount hyperbolically than nonsmokers, and, thus, were not more prone to time-inconsistent discounting.
  
  
  
  The results inform the interpretation of steep discounting among smokers and suggest that treatment approaches could be tailored to the type of discounting behavior that smokers exhibit.
authors.affiliation: a School of Economics , University of Cape Town , Cape Town , South Africa.
authors.forename: Andre
authors.initials: A
authors.lastname: Hofmeyr
authors.affiliation: b Department of Psychology , University of Southern California , Los Angeles , CA , USA.|c Neuroscience Graduate Program , University of Southern California , Los Angeles , CA , USA.|d Brain and Creativity Institute, University of Southern California , Los Angeles , CA , USA.
authors.forename: John
authors.initials: J
authors.lastname: Monterosso
authors.affiliation: e Department of Psychiatry and Biobehavioral Sciences , University of California Los Angeles , Los Angeles , CA , USA.|f Brain Research Institute, University of California Los Angeles , Los Angeles , CA , USA.|g Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles , Los Angeles , CA , USA.
authors.forename: Andy C
authors.initials: AC
authors.lastname: Dean
authors.affiliation: e Department of Psychiatry and Biobehavioral Sciences , University of California Los Angeles , Los Angeles , CA , USA.|g Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles , Los Angeles , CA , USA.
authors.forename: Angelica M
authors.initials: AM
authors.lastname: Morales
authors.affiliation: e Department of Psychiatry and Biobehavioral Sciences , University of California Los Angeles , Los Angeles , CA , USA.|g Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles , Los Angeles , CA , USA.|h Department of Psychology , University of California Los Angeles , Los Angeles , CA , USA.|i Steward & Lynda Resnick Neuropsychiatric Hospital , University of California Los Angeles , Los Angeles , CA , USA.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Bilder
authors.affiliation: e Department of Psychiatry and Biobehavioral Sciences , University of California Los Angeles , Los Angeles , CA , USA.|g Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles , Los Angeles , CA , USA.|j Lewis Center for Neuroimaging , University of Oregon , Eugene , OR , USA.
authors.forename: Fred W
authors.initials: FW
authors.lastname: Sabb
authors.affiliation: e Department of Psychiatry and Biobehavioral Sciences , University of California Los Angeles , Los Angeles , CA , USA.|f Brain Research Institute, University of California Los Angeles , Los Angeles , CA , USA.|g Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles , Los Angeles , CA , USA.|k Department of Molecular and Medical Pharmacology , University of California Los Angeles , Los Angeles , CA , USA.
authors.forename: Edythe D
authors.initials: ED
authors.lastname: London
mesh_terms: D000328:Adult; D002755:Choice Behavior; D065786:Delay Discounting; D005260:Female; D006801:Humans; D007175:Impulsive Behavior; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D012201:Reward; D000074285:Smokers / Q000523:psychology; D012907:Smoking / Q000523:psychology*; D011795:Surveys and Questionnaires; D055815:Young Adult
keywords: Mixture models; addiction; delay discounting; impulsivity; smoking