Published papers

Rosato A. and Tymula A. (2024) A novel experimental test of truthful bidding in second-price auctions with real objects, Journal of Behavioral and Experimental Economics, 111

Kettlewell N. and Tymula A. (2024) Heritability across different domains of trust, Journal of Economic Behavior and Organization, 219:549-563

Pastore C., Schurer S., Tymula A., Fuller N, Caterson I. (2023) Economic Preferences and Obesity: Evidence from a Clinical Lab-in-Field Experiment, Health Economics, 32:2147-2167

Kurtz-David, V., Alladi, V., Bucher, S., Brandenburger, A., Louie, K., Glimcher, P., & Tymula, A. (2023). Choosers Adapt Value Coding to the Environment, But Do Not Attain Efficiency.Proceedings of the Annual Meeting of the Cognitive Science Society, 45

Tymula A., Wang X., Imaizumi Y., Kawai T., Kunimatsu J., Matsumoto M. and Yamada H. (2023) Dynamic prospect theory – two core decision theories coexist in the gambling behavior of monkeys and humans,   Science Advances, 9(20)

Glimcher P. W. and Tymula A. (2023) Expected Subjective Value Theory (ESVT): A representation of decision under risk and certainty,  Journal of Economic Behavior and Organization, 207: 110-128

Kettlewell N., Rijsdijk F., Siribaddana S., Sumathipala A., Tymula A., Zavos H., Glozier N. (2023) The impact of war and tsunami on risk aversion: Evidence from Sri Lankan twins, accepted at  Applied Economics

Imaizumi Y., Tymula A., Tsubo Y., Matsumoto M. and Yamada H. (2022) A neuronal prospect theory model in the brain reward circuitry, Nature Communications, 13(5855)

Berger A. and Tymula A. (2022) Controlling ambiguity: The illusion of control in decision-making under risk and ambiguity [short poster presentation]  Journal of Risk and Uncertainty 10.1007/s11166-022-09399-4 

Cheung S. L., Tymula A., Wang X. (2022) Present Bias for Monetary and Dietary Rewards: Evidence from Chinese Teenagers, Experimental Economics, 25: 1202–1233 

Kettlewell N. and Tymula A. (2021) The Australian Twins Economic Preferences Survey, Twin Research and Human Genetics

Guo J. and Tymula A. (2021) Waterfall illusion in risky choice, European Economic Review, 139 

Heger S., Slonim R., Taush F. and Tymula A. (2021) Altruism among Consumers as Donors,  Journal of Economic Behavior and Organization, 189: 611-622

Tymula A. and Wang X. (2021) Increased risk-taking, not loss tolerance, drives adolescents’ propensity to gamble more under peer observation, [supplement], Journal of Economic Behaviour and Organization, 188:439-457

Gainsbury S. M., Black N., Blaszczynski A., Callaghan S., Clancey G., Starcevic V., Tymula A. (2020) Reducing Internet gambling harms using behavioural science: A stakeholder framework, Frontiers in Psychiatry, section Addictive Disorders 11:598589

Weinrabe A., Chung H., Tymula A., Tranand J., Hickie I. (2020) Economic Rationality in Young People with Emerging Mood Disorder, Journal of Neuroscience, Economics, and Psychology

Tymula (2019) Adolescents are more impatient and inconsistent, not more risk-taking when observed by peers – a comprehensive study of adolescent behavior under peer observation, Journal of Economic Behavior and Organisation, 166:735-750

Chung, H., Glimcher. P.W., Tymula, A. (2019) An Experimental Comparison of Risky and Riskless Choice – Limitations of Prospect Theory and Expected Utility Theory, American Economic Journal: Micro, 11(3):34-67

Rosato A. and Tymula A. (2019) Loss Aversion and Competition in Vickrey Auctions: Money Ain’t No Good, Games and Economic Behavior, 115: 188-208 

Tymula, A. and Whitehair, J. (2018) Young adults gamble less when observed by peers, Journal of Economic Psychology, 68:1-15

Yamada H., Louie K., Tymula A. and Glimcher P.W. (2018) Free choice shapes normalized value signals in medial orbitofrontal cortex, Nature Communications, 9(1):162

Chung H., Tymula A., Glimcher P. (2017) The Reduction of Ventrolateral Prefrontal Cortex Grey Matter Volume Correlates with Loss of Economic Rationality in Aging, Journal of Neuroscience, 37 (49) 12068-12077

Glimcher, P.W. and Tymula, A. (2017) Let the sunshine in? The effects of luminance on economic preferences, choice consistency and dominance violations. PLoS ONE, 12(8): e0181112

Tymula, A. (2017) Competitive Screening of Heterogenous Labor Force and Corporate Teamwork Attitude. Journal of Institutional and Theoretical Economics, 173(3), 523-547

Grubb M., Tymula A., Gilaie-Dotan S., Glimcher P. and Ifat Levy (2016) Neuroanatomy accounts for age-related changes in risk preferences. Nature Communications, 7

Tymula, A., Plassmann, H. (2016) Context-dependency in valuation. Current Opinion in Neurobiology, 40: 59-65

Tymula, A., Woelbert, E., Glimcher, P.W. (2016) Flexible Valuations for Consumer Goods as Measured by the Becker-DeGroot-Marschak Mechanism. Journal of Neuroscience, Psychology, and Economics,  9(2):65-77.

Gilaie-Dotan, S.,⁺ Tymula, A.,⁺ Cooper, N., Kable, J., Glimcher, P.W., Levy, I. (2014) Neuroanatomy predicts individual risk attitudes. Journal of Neuroscience, 34(37) (⁺shared first author, featured article)

Tymula, A., Rosenberg Belmaker, L.A., Ruderman, L., Glimcher, P.W., Levy, I. (2013) Like cognitive function, decision-making across the lifespan shows profound age-related changes. Proceedings of the National Academy of Sciences, 110(42)

Yamada, H.⁺, Tymula, A.⁺, Louie, K., Glimcher, P.W. (2013) Thirst-dependent risk preferences in monkeys identify a primitive form of wealth. Proceedings of the National Academy of Sciences, 110(39) (⁺shared first author)

Großer, J., Reuben, E., Tymula, A. (2013) Political quid pro quo agreements: An experimental study. American Journal of Political Science, 57(3):582-597

Tymula, A.⁺, Rosenberg Belmaker, L.A.⁺, Roy, A., Ruderman, L., Manson, K., Glimcher, P.W., Levy, I. (2012) Adolescents’ risk-taking behavior is driven by tolerance to ambiguity. Proceedings of the National Academy of Sciences 109 (42):17135-17140 (⁺ shared first author)

Levy, I., Rosenberg-Belmaker, L.A., Manson, K., Tymula, A., Glimcher, P.W. (2012) Measuring the subjective value of risky and ambiguous options using experimental economics and functional MRI methods. Journal of Visualized Experiments, 67

Kuhnen, C., and Tymula, A. (2012) Feedback, self-esteem and performance in organizations. Management Science, 58(1):94-113

Published book chapters

Tymula A. (2019). Brain Morphometry for Economists: How do Brain Volume Constraints Affect Our Choices? in Biophysical Measurement in Experimental Social Science Research, Foster (Eds.), ELSEVIER

Tymula A. and Glimcher P.W. (2018). Emotions through the lens of economic theory. In Fox, A. S., Lapate, R. C., Shackman, A. J. & Davidson, R. J. (Eds.), The Nature of Emotion. Fundamental questions (2nd Edition). New York: Oxford University Press 

Tymula A. (2017) Tolerance for ambiguity. In Moghaddam F.M. (Ed.) The SAGE Encyclopaedia of Political Behavior, SAGE Publications, Thousand Oaks CA 

Other writing

Tymula A. and Wang X. (2021) The years of living dangerously: can adolescents be encouraged away from risky behaviour? Sydney Business Insights

Tymula A. (2016) Financial gamble? My brain made me do it. The Conversation 

Tymula, A. and Glimcher, P.W. (2015) Are adolescents really risk-takers? Most adults say yes, but the science is starting to say no. Frontiers for Young Minds.  3:3. 

• featured on Scientific American Blog Network
• written for the Young Minds of the 2014 USA Science and Engineering Festival

Tymula A. (2014) Explainer: neuroeconomics, where science and economics meet. The Conversation 

Book review of After Phrenology: Neural Reuse and the Interactive Brain, Michael L. Anderson. The MIT Press, Cambridge, MA, USA (2014) in Journal of Economic Psychology, Volume 51, December 2015, p. 279–280

Papers under review

Cheung S., Tymula, A. and Wang X. (2023) Quasi-hyperbolic present bias: A meta-analysis [short poster presentation] revision requested from Management Science

Quasi-hyperbolic discounting is one of the most well-known and widely-used models to capture self-control problems in the economics literature. The underlying assumption of this model is that agents have a “present bias” toward current consumption such that all future rewards are downweighed relative to rewards in the present (in addition to standard exponential discounting for the length of delay). We report a meta-analytic dataset of estimates of the present bias parameter based on searches of all major research databases (62 papers with 81 estimates in total). We find that the literature shows that people are on average present biased for both monetary rewards (beta=0.82, 95% confidence interval of [0.74, 0.90]) and non-monetary rewards (beta=0.66, 95% confidence interval of [0.51, 0.85]) but that substantial heterogeneity exists across studies. The source of this heterogeneity comes from the subject pool, elicitation methodology, geographical location, payment method, mode of data collection (e.g. laboratory or field), and reward type. There is evidence of selective reporting and publication bias in the direction of overestimating the strength of present-bias (making estimates smaller), but present bias still exists after correcting for these issues (for money beta=0.87 with 95% confidence interval of [0.82, 0.92] after correcting for selective reporting).

 Kurtz-David V., Sinha S., Alladi V., Bucher S., Brandenburger A., Louie K., Glimcher P. and Tymula A. (2024) A Tale of Two Environments: Divisive Normalization and the (In)Flexibility of Choice 

The Divisive Normalization (DN) function has been described as a “canonical neural computation” in the brain that achieves efficient representations of sensory and choice stimuli. Recent theoretical work indicates that it efficiently encodes a specific class of Pareto-distributed stimuli. Does the brain shift to different encoding functions in other types of environments, or is there evidence for DN encoding in other types of environments? In this paper, using a within-subject choice experiment, we show evidence of the latter. Our subjects made decisions in two distinct choice environments with choice sets either drawn from a Pareto distribution or from a uniform distribution. Our results indicate that subjects’ choices are better described by a divisive coding strategy in both environments. Moreover, subjects appeared to calibrate a DN function to match, as closely as possible, the actual statistical properties of each environment. These results suggest that the nervous system may be constrained to use divisive representations under all conditions.

 Cheung S., MacGibbon K., Milin-Byrne A., Tymula A. (2024) Quasi-exponential discounting 

Alternatives to the standard model of time preference typically relax the assumption of an exponential discount function while retaining the framework of discounted utility. We report novel behavioural data inconsistent with this approach. Illustrating this, we estimate highly significant “present bias”, despite our data exhibiting stationarity. The paradox is resolved by relaxing discounted utility itself to allow discounting to be context dependent. We propose quasi-exponential discounting (QED), a fixed penalty applied to all episodes of delay, as a particularly simple model of this type and show that it provides an excellent approximation to the best fit to our data.

 Schurer S., Tymula A., Wang X., Fuller N., and Caterson I. (2024) Impatience and present bias do not determine weight loss in obesity: Evidence from lab-in-field and nationally representative data 

Behavioral economic theory attributes the inability to lose weight to impatience and present bias, assuming they lead to excessive food consumption and inadequate exercise. We use data from a large-scale lab-in-field study that tracks 293 participants with obesity who attempted to improve their health as part of a 12-month randomized controlled trial conducted in a clinical setting. Consistent with behavioral economic theory, we find that trial participants who are less impatient are more likely to complete the trial. However, there is no evidence that participants who are less impatient or less present-biased are more successful in reducing body fat or weight. We replicate that a person’s impatience does not predict their intended weight change over a period of one year using a nationally representative data of 6,118 adults with obesity. Our results suggest that obesity is not just a behavioral condition. Treatments that focus on correcting individual’s impatience or self-control alone may not be the right approach for weight loss in clinically-relevant populations.

Phillips L., Tymula A., and Wang X. (2024) The Effect of Disadvantage on Decision Making Under Uncertainty 

Discrimination based on race, gender, or religion is a well-documented phenomenon that leads to disadvantageous financial, labor market, academic, and social outcomes for those who experience it. These disadvantages are known to arise from decisions made by those who discriminate. But does experiencing discrimination also alter our own decision-making? To explore this question, we designed a novel experiment to examine how discrimination affects investment decisions in ambiguous and risky assets. In our within-subject study, we introduced discrimination by varying the probability of receiving a small performance bonus (5% vs 95% chance). We found that after experiencing discrimination (only 5% chance of a bonus), participants invested less in ambiguous assets but their investments in risky assets remained unchanged. We examined whether an increase in wealth, much higher than the monetary cost of discrimination, and previous experience of discrimination mitigate the effects of our discrimination treatment. Our research underscores the importance of accounting for additional indirect costs of discrimination.

Levy J., Ru O., and Tymula A. (2024) The gender reference point gap: Evidence from a representative sample 

While women are generally more risk-averse than men, the reasons remain unclear. Inspired by efficient coding literature, we hypothesize that women’s lower financial risk tolerance is due to lower reference points. We measured financial reference points in a representative US sample using a range of unincentivized and incentivized methods. Our findings show that women consistently have lower reference points, leading to more risk-averse behavior. We explore potential reasons for this and its policy implications.

Tymula A. and Yamada H. (2024) Neural and behavioral probability weighting function 

Recent theoretical models challenge the existence of a probability weighting function as it was traditionally conceived in Prospect Theory in ways that are not straightforward to test using choice data. This study transcends these constraints by directly observing probability distortions in the brain, free from utility confounds. Utilizing a unique dataset comprising 64,175 decision trials and 78,067 neural measurement trials, we pinpoint neural activity (a basic biological decision processing unit) that exclusively encodes probability, independent of payoff magnitudes. Our results demonstrate that neural probability weighting functions diverge from those estimated behaviorally under conventional assumptions. Furthermore, incorporating a biologically realistic utility function enhances our ability to reconstruct neural probability weighting from observed choices, offering direct biological evidence on the bases of economic decision-making.

Kettlewell N. and Tymula A. (2024) Heritability of different types of overconfidence 

Incorrect estimation of own absolute and relative abilities is common and can have detrimental effects on a person’s educational, social, employment, and financial outcomes. It is not yet fully understood from where interpersonal differences in overconfidence emerge. In this paper, we estimate the heritability of two types of overconfidence, overestimation and overplacement, in a sample of 1120 twins. We find that the genetic heritability of both types of overconfidence is about 19% and that most of the interindividual variation in overconfidence is due to individual-specific environmental factors.

Kettlewell N., Tymula, A. and Yoo H. (2023) The heritability of economic preferences 

We study the heritability of risk, uncertainty, and time preferences using a field experiment with a large sample of adult twins. We also offer a meta-analysis of existing findings. Our field study introduces a novel empirical approach that marries behavioral genetics with structural econometrics. This allows us to, for the first time, quantify the heritability of economic preference parameters directly without employing proxy measures. Our incentive-compatible experiment is the first twin study to elicit all three types of preferences for the same individual. Compared to previous studies, we find a greater role of genes in explaining risk and uncertainty preferences, and of the shared familial environment in explaining time preferences. Time preferences appear more important from policy and parenting perspectives since they exhibit limited genetic variation and are more than twice as sensitive to the familial environment as risk and uncertainty preferences.

Kettlewell N., Levy J., Tymula A., Wang X. (2023) The gender reference point gap 

Studies have frequently found that women are more risk averse than men. In this paper, we depart from usual practice in economics that treats risk attitude as a primitive, and instead adopt a neuroeconomic approach where risk attitude is determined by the reference point which can be easily estimated using standard econometric methods. We then evaluate whether there is a gender difference in the reference point, explaining the gender difference in risk aversion observed using traditional approaches. In our study, women make riskier choices less frequently than men. Compared to men, we find that women on average have a significantly lower reference point. By acknowledging the reference point as a potential source of gender inequality, we can begin a new discussion on how to address this important issue.

Akbari M., Alladi V., Je H. and Tymula A (2023) Ambiguity vulnerability 

We theoretically define and empirically investigate a new notion: ambiguity vulnerability. Ambiguity vulnerability posits that individuals exhibit greater risk aversion in their decisions when faced with a background (that is beyond an individual’s control) prospect that has unknown probabilities (background ambiguity) than one with known probabilities (background risk). We find empirical evidence of ambiguity vulnerability, with individuals investing 11% less when faced with background ambiguity compared to background risk. We provide evidence on the relationship between utility shape and risk and ambiguity vulnerability. Finally, our results suggest that financial stress could be perceived as a form of background uncertainty, potentially reducing individuals’ profitable investments.