Abstract
A probability weighting function (w(p)) is considered to be a nonlinear function of probability (p) in behavioral decision theory. This study proposes a psychophysical model of probability weighting functions derived from a hyperbolic time discounting model and a geometric distribution. The aim of the study is to show probability weighting functions from the point of view of waiting time for a decision maker. Since the expected value of a geometrically distributed random variable X is 1/p, we formulized the probability weighting function of the expected value model for hyperbolic time discounting as w(p) = (1 − k log p)−1. Moreover, the probability weighting function is derived from Loewenstein and Prelec's () generalized hyperbolic time discounting model. The latter model is proved to be equivalent to the hyperbolic-logarithmic weighting function considered by Prelec () and Luce (). In this study, we derive a model from the generalized hyperbolic time discounting model assuming Fechner's () psychophysical law of time and a geometric distribution of trials. In addition, we develop median models of hyperbolic time discounting and generalized hyperbolic time discounting. To illustrate the fitness of each model, a psychological experiment was conducted to assess the probability weighting and value functions at the level of the individual participant. The participants were 50 university students. The results of individual analysis indicated that the expected value model of generalized hyperbolic discounting fitted better than previous probability weighting decision-making models. The theoretical implications of this finding are discussed.
Introduction
Probability weighting functions (w(p)) are widely known in behavioral decision theory and behavioral economics. A probability weighting function is considered to be a nonlinear function of probability (p). There are several probability weighting decision-making models for representing probability weighting functions (e.g., Tversky and Kahneman, ; Prelec, ; Gonzalez and Wu, ; Takahashi, ; Zhang and Maloney, ; Takemura, ). However, most of the proposed models are not related to traditional psychological theories such as psychophysics and learning theory, with the exception of studies by Prelec and Loewenstein (), Tversky and Kahneman (), Kusev et al. (), and Takahashi (). Prelec and Loewenstein () first pointed out that there are common properties between risky and intertemporal choices from an axiomatic point of view. They illustrated that the choice patterns of risky and intertemporal choices are very similar in terms of their axiomatic properties. From this point, they suggested that there are some common behavioral foundations between the probability weighting function and the time discounting function. Importantly, they illustrated some common axiomatic properties between the probability weighting function and the time discounting function, although no psychological account was given.
In prospect theory (proposed by Kahneman and Tversky, ), the probability weighting function has psychophysical foundation as well as the value function. Additionally, in cumulative prospect theory (proposed by Tversky and Kahneman, ), the probability weighting model parameter represents “probability discriminability” and “diminishing sensitivity”—assumptions derived from psychophysical research. Furthermore, the probability-weighting model in Kusev et al. () accommodates a memory parameter (accessibility to events from memory). Their results revealed evidence that exaggerated risk is caused by the accessibility of events in memory; in other words, the weighting function varies as a function of the accessibility of events. This suggests that people's experiences of events leak into decisions even when risk information is explicitly provided. In addition, Takahashi () combined psychophysical theory with Cajueiro's () q-exponential function for explaining time discounting, proposed a new general model, and then derived Prelec's () probability weighting function as a special case. The merit of combining a probability weighting model with a time discounting model is to create an integrated human decision model. The time discounting model and decision under risk, whose probability distribution is known, are both important areas in behavioral decision research. However, there seems to be a strong connection between them.
The purpose of the present study is to show several probability weighting functions from the viewpoint of a decision maker's waiting time to receive an outcome. The study proposes another type of probability weighting function derived from the hyperbolic time discounting model in a simpler form. We assume only the hyperbolic time discounting function and Fechner's () logarithmic psychophysical function. By the assumptions of the geometric distribution of waiting time and Fechner's () law, we provide a new account of Prelec's () probability weighting function.
Last, we perform an experimental study to illustrate the fitness of our models and previous models. Concerning the empirical research on probability functions, important research has been conducted by Stott (). In particular, Stott () reviewed eight different forms of the probability weighting function (linear model, power model, log-odds model, Tversky–Kahneman model, Wu–Gonzalez model, two versions of Prelec's model, and non-parametric model) and reported parameters estimated from multiple empirical papers over a period of 10 years. He also reported an extensive empirical study for 96 participants by utilizing 90 different gamble stimuli. His study compared fits on a total of 256 combinations of cumulative prospect theory functional forms, including eight probability functions, eight value function forms, and four choice functions. Based on this study, he concluded that the best model has a risky weighting function of the simple version of Prelec's () model, a power value function, and a logit choice function. We also examined the Prelec () model using the power function for a value function by comparing the proposed model and some previous models. Although the number of participants was limited (total of 50 participants), Prelec's () general version of the probability weighting model fitted our data better than the other models did. This finding shows that the best model is the probability weighting function based on Loewenstein and Prelec's () generalized hyperbolic time discounting model.
Probability weighting function based on prospect theory
Nonlinear utility theory was proposed to explain several anomalies of expected utility theory, such as the Allais paradox (Allais, ). This body of theory is a generalization of expected utility theory (Tamura et al., ; Starmer, ). This theory is called the nonlinear utility theory (Fishburn, ; Edwards, ) or generalized expected utility theory (Quiggin, ) in the field of economics, although it is mathematically equivalent to the theory of non-Lebesgue integration in fuzzy measure theory in the field of engineering (Sugeno and Murofushi, ; Takemura, ). Nonlinear utility theory often assumes a non-additive probability weighting function that converts probabilities for which additivity does not hold, even if probability information is given for decision making under risk, such as in the case of the Allais paradox. A non-additive probability is sometimes referred to as a “capacity,” but in some cases (e.g., in the field of engineering) is called a “fuzzy measure.” Its mathematical definition is the same despite these varying names. A non-additive probability refers to a set function, w: 2Ω → [0, 1] from an aggregate consisting of subsets of a nonempty set, Ω, to a closed interval, [0,1], which is also a set function that satisfies both a boundedness condition (w(ϕ) = 0, w(Ω) = 1) and a monotonicity condition (if the relation of subsets E and F of Ω is E ⊆ F, then the relation w(E) ≦ w(F) is satisfied). A non-additive probability is so named because it does not necessarily satisfy the conditions of additivity.
Moreover, a non-additive probability weighting function in prospect theory has the following properties: w(0) = 0 and w(1) = 1; it is of the form shown in Figures 1, 2. Assuming that the probability weighting function is w and that the probability is p, the probability weighting function has the following qualitative characteristics.
It satisfies the condition of w(p) + w(1 − p) ≤ 1.
It overvalues the probability when the probability is very low, engendering the relation of w(p) > p.
It shows non-proportionality—i.e., .
It has non-continuity near the endpoints.
Figure 1
Figure 2

Probability weighting function derived from hyperbolic discounting model.
Tversky and Kahneman (
Based on the results of the selections in this experiment, they performed a nonlinear regression analysis and estimated 0.88 for both α and β, and 2.55 for λ. The fact that the estimated values of α and β are less than one indicates that the value function is concave downward in both the areas of gain and loss. The estimated value of λ suggests that loss has an impact that is approximately twice as great as that of profit, implying substantial strength for loss aversion.
They further considered the following functions as specific decision weight functions, W+ and W−, of cumulative prospect theory, and estimated the form of the decision weight functions illustrated in Figure 1 from this selection experiment.
Another well-known two-parameter model was proposed by Prelec (
where .
In most empirical studies of probability weighting functions, assuming δ equals 1, a one-parameter model is used, which can be described as follows:
Probability weighting function derived from hyperbolic time discounting
Hyperbolic discounting is a mathematical model devised as an improvement over the exponential discounting model, a time-consistent model of discounting. Hyperbolic discounting can be described as follows:
where f (D) is the discount factor that multiplies the value of the reward, D is the delay in the reward, and k is a parameter governing the degree of discounting. In this study, we derive the logarithmic hyperbolic probability weighting function from f (D), assuming that the trial is a geometrically distributed random variable and that the delay is evaluated using Fechner's (
We assume that the probability weighting function, w(p), is psychologically related to the delay discounting function, f (D). The key assumption in this is equating delay, D, with the expected number of Bernoulli trials to obtain one success (1/p), and considering that the perceived delay is a logarithmic function of the delay based on Fechner's (
Because the odds of receiving probabilistic gain ((1-p)/p)) is equal to the expected number of Bernoulli trials to obtain one success (1/p) − 1 (i.e., (1/p) −1), we have a similar assumption by Rachlin et al. (
Let X be the number of Bernoulli trials required to obtain one success, supported on the set {1, 2, 3, … }. This is the probability that the first occurrence of success requires k independent trials, each with probability p of success. If the probability of success on each trial is p, then the probability that the kth trial is the first success is:
The probabilities form a geometric sequence. The expected value of a geometrically distributed random variable X is 1/p, and the variance is (1 − p) ∕ p2.
Assuming Fechner's (
The probability weighting function derived from hyperbolic time discounting (Figure 2) is:
where p is the probability, k is a constant, and k > 0.
The indicator −ln p (=ln (1∕p)) is also related to the median of trials to some extent. That is, the median of the trials is:
Since the geometric distribution is skewed, −log p is considered to be an approximation of the median of trials. On this interpretation, the probability of the weighting function is:
where p is probability, k is a constant, and k > 0.
Although the median model is related to the hyperbolic model, the median model in Equation (8) will be discussed elsewhere in more detail.
Probability weighting function derived from generalized hyperbolic time discounting
The probability weighting function is also derived from Loewenstein and Prelec's (
Their model is as follows:
Letting α = k and γ/α = β, their model can be written as follows:
Assuming Fechner's (
The probability weighting function derived from the generalized hyperbolic time discounting Equation (6) is as follows:
where p is probability, k is a positive constant, and β is a negative constant.
The model (11) is the same as the hyperbolic-logarithmic weighting function considered by Prelec (
We also proposed a new psychophysical model based on generalized hyperbolic time discounting. Since the geometric distribution is skewed, as noted previously, −log p is considered to be an approximation of the median of trials. On this interpretation, the probability of the weighting function is as follows:
where p is probability, k is a positive constant, and β is a negative parameter.
Method of psychological experiment
We adopted experimental methods similar to those of previous studies (Tversky and Kahneman,
Participants
We report data for 50 participants (35 females and 15 males, aged 19–24 years). All participants were undergraduate students in psychology. They were paid 2000 Japanese yen (about 20 dollars) for participating in four sessions that lasted 1 h and 30 min each.
Materials
The basic design consisted of 15 two-outcome wagers with 11 levels of probability associated with the maximum outcome, in the same manner of the study by Gonzalez and Wu (
Procedure
A simplified computer program following the procedure outlined in Tversky and Kahneman (
Figure 3

An example of presented format in the experiment.
Results and discussion of the experiment
Reliability for the nine repeated wagers was measured by intraclass correlation. The median of 50 intraclass correlations computed for the individual subject data was 0.98, with a range of 0.36–1.00. The experimental procedure appears to have elicited relatively high levels of reliability for most participants. The median of the reliability was slightly higher than that for the findings of Gonzalez and Wu (
As suggested by Gonzalez and Wu (
Interpolate for vi(CE): using the estimates of v() for the current iteration, which are based on the eight stimuli money amounts, interpolate to find vi(CE) for each of the 165 certainty equivalents; these 165 vi(CE) values will be used as “data” for the estimation in Steps 2 and 3.
Fix all v() values to the current iteration values and estimate the eleven wi values using an iteratively reweighted, nonlinear least-squares algorithm.
Fix the 11 w() values to the current iteration values and estimate the eight vi() values using an iteratively reweighted, nonlinear least-squares algorithm.
If an optimum value is found, then stop; otherwise, increment iteration counter i and repeat.
We first computed the value function parameter assuming the power function using the abovementioned nonlinear least-squares algorithm for the median values of certainty equivalents for all participants. The estimated value of power was 0.80. We then computed the power value for each participant. The median power value was 0.85 (the lowest was 0.34 and the highest was 1.00). The power value in the study by Tversky and Kahneman (
It should be noted that the value function is convex for the loss domain, as indicated by Tversky and Kahneman (
To examine whether the finding in that study was replicated or not, we compared the value of a parameter of this study to the corresponding value in the previous study. The value of γ in the study of Tversky and Kahneman (
We fitted the individual choice data with not only the probability weighting function proposed by Tversky and Kahneman (
We used the same procedure as in the study by Gonzalez and Wu (
Figure 4

The cumulative distributions of the AIC values for the six models.
Figure 5

The stacked bar chart of the AIC ranks for the six models.
We also analyzed individual data, and computed AIC and BIC for each participant. Since patterns of AIC and BIC were similar for each participant data, we only analyzed the AIC values. We coded the rank of the AIC value of the model for each participant in a manner similar to that shown in Stott's (
This result suggests that the generalized hyperbolic model (Prelec,
We also provide individual fits of all 46 participants in a single plot for each model of interest in Figure 6. Histograms of the estimated parameters of all six models across 46 participants are shown in Figure 7. In Figure 7, the following parameters were shown: (A) Tversky and Kahneman (
Figure 6

Individual fits of all 46 participants in a single plot for each model.
Figure 7

Histograms of the estimated parameters of all six models across 46 participants: (A) Tversky and Kahneman (
Figure 8

The estimated probability weighting function of the outlier (Participant 7).
Conclusion
The present study proposed a probability weighting function derived from a hyperbolic time discounting model by assuming a geometric distribution. Moreover, our probability weighting function was derived from Loewenstein and Prelec's (
There are two primary contributions of this study. First, we derived the probability weighting function based on the generalized hyperbolic time discounting function. Second, we demonstrated the empirical study comparisons that fitted for six different probability weighting functions for 50 participants each corresponding to 165 unique gambles. This paper therefore provides theoretical and empirical support for a psychological interpretation of the probability weighting function from a time discounting perspective.
Further theoretical and empirical studies will be required to examine the shape of the probability weighting function. The results of the psychological experiment indicated that the expected value model of generalized hyperbolic discounting was a better fit than previous probability weighting decision-making models. However, we do not think that strong conclusions are ill advised owing to the limited number of participants, as compared to those in Stott's (
Funding
This study was supported by JSPS Grant-in-Aid for Scientific Research (A), No.24243061.
Conflict of interest statement
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Statements
Author contributions
KT supervised the project, and made mathematical models and wrote the manuscript. HM conducted the experiments and analyzed the data.
Acknowledgments
We would like to thank Yuki Tamari, Takashi Ideno, Takayuki Sakagami, Yutaka Nakamura, and referees of this journal for valuable comments.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Supplementary material
The Supplementary Material for this article can be found online at: http://journal.frontiersin.org/article/10.3389/fpsyg.2016.00778
References
1
AllaisM. (1953). Le comportement de l'homme rationnel devant le risque: critique des postulats et axiomes de l'école Américaine. Econometrica21, 503–546. 10.2307/1907921
2
CajueiroD. O. (2006). A note on the relevance of the q-exponential function in the context of intertemporal choices. Phys. A364, 385–388. 10.1016/j.physa.2005.08.056
3
EdwardsW. (1992). Utility Theories: Measurements and Applications. Boston, MA: Kluwer Academic Publishers.
4
FechnerG. T. (1860). Elemente Der Psychophysik.Leipzig: Breitkopf & Hartel.
5
FishburnP. C. (1988). Nonlinear Preference and Utility Theory. Baltimore, MD: Johns Hopkins University Press.
6
GonzalezR.WuG. (1999). On the shape of the probability weighting function. Cogn. Psychol.38, 129–166. 10.1006/cogp.1998.0710
7
JonesS.OaksfordM. (2011). Transaction problem content in cost discounting: parallel effects for probability and delay. J. Exp. Psychol. Learn. Mem. Cogn.37, 739–747. 10.1037/a0022219
8
KahnemanD.TverskyA. (1979). Prospect theory: an analysis of decision under risk. Econometrica47, 263–292. 10.2307/1914185
9
KusevP.van SchaikP. (2011). Preferences under risk: content-dependent behavior and psychological processing. Front. Psychol.2:269. 10.3389/fpsyg.2011.00269
10
KusevP.van SchaikP.AytonP.DentJ.ChaterN. (2009). Exaggerated risk: prospect theory and probability weighting in risky choice. J. Exp. Psychol. Learn. Mem. Cogn.35, 1487–1505. 10.1037/a0017039
11
LoewensteinG. F.PrelecD. (1992). Anomalies in intertemporal choice: evidence and an interpretation. Q. J. Econ.107, 573–597. 10.2307/2118482
12
LuceR. D. (2001). Reduction invariance and prelec's weighting functions. J. Math. Psychol.45, 167–179. 10.1006/jmps.1999.1301
13
PrelecD. (1998). The probability weighting function. Econometrica66, 497–527. 10.2307/2998573
14
PrelecD.LoewensteinG. (1991). Decision making over time and under uncertainty: a common approach. Manage. Sci.37, 770–786. 10.1287/mnsc.37.7.770
15
QuigginJ. (1993). Generalized Expected Utility Theory: The Rank Dependent Model. Boston, MA: Kluwer Academic Publishers.
16
RachlinH.BrownJ.CrossD. (2000). Discounting in judgments of delay and probability. J. Behav. Decis. Mak.13, 145–159. 10.1002/(SICI)1099-0771(200004/06)13:2<145::AID-BDM320>3.0.CO;2-4
17
RachlinH.RaineriA.CrossD. (1991). Subjective probability and delay. J. Exp. Anal. Behav.55, 233–244. 10.1901/jeab.1991.55-233
18
StarmerC. (2000). Developments in non-expected utility theory: the hunt for descriptive theory of choice under risk. J. Econ. Lit.38, 332–382. 10.1257/jel.38.2.332
19
StottH. (2006). Cumulative prospect theory's functional menagerie. J. Risk Uncertain.32, 101–130. 10.1007/s11166-006-8289-6
20
SugenoM.MurofushiT. (1993). Koza Faji 3: Faji Sokudo (Course Fuzzy 3: Fuzzy Measure). Tokyo: The Nikkan Kogyo Shimbun.
21
TakahashiT. (2011). Psychophysics of the probability weighting function. Phys. A Stat. Mech. Appl.390, 902–905. 10.1016/j.physa.2010.10.004
22
TakemuraK. (2014). Behavioral Decision Theory: Psychological and Mathematical Descriptions of Human Choice Behavior. Tokyo: Springer.
23
TamuraH.NakamuraY.FujitaS. (1997). Kouyou Bunseki no Suuri to Ouyou (Mathematical Principles and Application of Utility Analysis). Tokyo: Corona Publishing.
24
TverskyA.KahnemanD. (1992). Advances in prospect theory: cumulative representation of uncertainty. J. Risk Uncertain.5, 297–323. 10.1007/BF00122574
25
WuG.GonzalezR. (1996). Curvature of the probability weighting function. Manage. Sci.42, 1676–1690. 10.1287/mnsc.42.12.1676
26
ZhangH.MaloneyL. T. (2012). Ubiquitous log odds: a common representation of probability and frequency distortion in perception, action, and cognition. Front. Neurosci.6:1. 10.3389/fnins.2012.00001
Summary
Keywords
probability weighting function, hyperbolic discounting, prospect theory, decision under risk, probability judgment
Citation
Takemura K and Murakami H (2016) Probability Weighting Functions Derived from Hyperbolic Time Discounting: Psychophysical Models and Their Individual Level Testing. Front. Psychol. 7:778. doi: 10.3389/fpsyg.2016.00778
Received
16 October 2015
Accepted
09 May 2016
Published
26 May 2016
Volume
7 - 2016
Edited by
Holmes Finch, Ball State University, USA
Reviewed by
Richard S. John, University of Southern California, USA; Martin Lages, University of Glasgow, UK; Petko Kusev, Kingston University London, UK
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© 2016 Takemura and Murakami.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Kazuhisa Takemura kazupsy@waseda.jp
This article was submitted to Quantitative Psychology and Measurement, a section of the journal Frontiers in Psychology
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