Scoring the Monetary Choice Questionnaire using logistic regression
Version 1.0b
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^mcqscore^ response_varlist, ^id(^id_variable^)^
^saving(^out_filename^)^ [^nojk^]
Description
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MCQScore scores the Monetary Choice Questionnaire (questions in
standard order), which uses a hyperbolic decay function to summarize
the degree to which time discounts the value of a delayed reward.
The scale parameter k is used as a measure of impulsivity.
Conventional scoring requires a lot of hand labor, identifying
indifference points where a subject's behavior changes from
preferring an immediate to a delayed reward. Instead, we use
logistic regression to identify a contour where the probability of
choosing either reward is 0.5, identifying in turn the corresponding
hyperbolic function. Logistic regression is applied to raw binary
choices from the survey, modeling the probability of choosing the
delayed reward in response to time and a transformation of the reward
ratio. The estimate of k is obtained as a ratio of the two betas.
Output will include log-k estimates for small, medium, and large
delayed reward sizes, a pooled log-k estimate and the component betas,
and optionally, a jackknife estimate of standard error for the pooled
log-k estimate and a bias-reduced estimate.
Two other ado files must be included for this routine to run. The
first is ^mcqlik.ado^, the penalized likelihood function that keeps
the parameter estimates in bounds. The second is ^mcq2long.ado^,
which transforms the data to long format, and associates question
numbers with reward values.
Please note that this is a first release. Please contact me with errors.
^response_varlist^ is required. It lists the names of the
variables containing the responses to
the MCQ in standard order. Data must
be 0s and 1s representing the choice
of the delayed reward. Data must also
be in wide format, with one line of
data per subject. Variable naming
should conform to the following
convention: use a common root with the
question number 1, 2, .. 27, on the
end of the name.
Options
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^id^ is required. It contains the name of the
subject identifier.
^saving^ is required. It is the name of an output
file for saving results.
^nojk^ is optional. By default, the jackknife
procedure is run. nojk prevents this.
Examples
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mcqscore choice1-choice27, id(subject)
saving(d:\discounting\my_outfile) nojk
mcqscore c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13 c14 c15 c16
c17 c18 c19 c20 c21 c22 c23 c24 c25 c26 c27, id(idname)
saving(d:\mcq\outputfile)
References
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Wileyto, E.P., Audrain-McGovern, J., Epstein, L.H., & Lerman,
C. (In Press) Using Logistic Regression to Estimate Delay-
Discounting Functions. Behavior Research Methods,
Instrumentation, & Computers.
Kirby, K.N., Petry, N.M., & Bickel, W.K. (1999) Heroin addicts
have higher discount rates for delayed rewards than non-
drug-using controls. Journal of Experimental Psychology:
General, 128, 78-87.
Author
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E. Paul Wileyto, Ph.D.
Assistant Professor of Biostatistics
Tobacco Use Research Center
School of Medicine, U. of Pennsylvania
3535 Market Street, Suite 4100
Philadelphia, PA 19104-6068
215-746-7147
Fax: 215-746-7140
epw@mail.med.upenn.edu